Analytical Studies	 Series 3 

Number 15 

Trendsin 

“Prematurity” 

United States: 1950-67 

An analysis of the trend in live births registered in the United 

States, 1950-67 by weight at birth and period of gestation, including an assessment of the quality of the data. Other factors, 

such as age of mother, plurality, sex, and delivery in hospi~ls 

are included insofar as they have a bearing on the trends. 

DHEW Publication No. (HSM) 72-1030 

U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE 

Public Health Service 

Health Services and Mental Health Administration 

National Center for Health Statistics 

Rockvill e, Md. Jonuary 1972 
Vital and Health Statistics-Series 3-No. 15 

For sale by the Superintendent of Docummts, U.S. Government Prhrtfng Office, Wsshfngton, D.C. 20402- Prioe 55 cents 
NATIONAL CENTER FOR HEALTH STATISTICS 

THEODORE D. WOOLSEY, Director 

PHILIP S. LAWRENCE, SC.D., Associate Director 

OSWALD K. SAGEN, Ph.D., Assistant Directorfor Health Statistics Development 

WALT R, SIMMONS, M.A,, Assistant Director for Research and Scientific Development 

JAMES E. KELLY, D.D.S., Dental Advisor 

EDWARD E. MINTY, Executive Officer 

ALICE HAYWOOD, Information Officer 

OFFICEOF HEALTHSTATISTICS ANALYSIS 

IWAO M. MORIYAMA, Ph. D., Director 

DEAN E. KRUEGER, M.S., Deputy Director 

Vital and Health Statistics-Series 3-No. 15 

DHEW Publication No. (HSM) 72-1030 

Library of Congress Catalog Card Number 70-610274 
CONTENTS


Page 

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...1


Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...3


SourceofData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4


CompletenessofData. . . . . . . . . . . . . . . . . . . . . . . . . ...5


AccuracyofData . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5


Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...8


PeriodofGestation . . . . . . . . . . . . . . . . . . . . . . . . . . . ...8


Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...8


Color, . .. o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..10


Future Prospects . . . . . . . . . . . . . . . . . . .. . . . . . . . . ...11


WeightatBirth .’....... . . . . . . . . . . . . . . . . . . . . . ...11


Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...11


FutureProspecti . . . . . . . . . . . . . . . . . . . . . . . . . . . ...13


WeightatBirthandPeriodofGestation . . . . . . . . . . . . . . . . . . . . 14


AreasReportingLMP . . . . . . . . . . . . . . . . . . . . . . . . . ...14


Areas ReportingWeeks of Gestation . . . . . . . . . . . . . . . . . . . . 16


AgeofMother . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...17


Birth Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...19


Plurality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...19


Sex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...20


P1aceofBirthandAttendant. . . . . . . . . . . . . . . . . . . . . . ...20


InternationalCompariso n... . . . . . . . . . . . . . . . . . . . . . ...26


SummaryandConclusion . . . . . . . . . . . . . . . . . . . . . . . . . ...27


Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...27


Quality of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...28


Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...29


References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...30


ListofDetailedTables . . . . . . . . . . . . . . . . . . . . . . . . . . . ...33


TechnicalAppendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...47


DefinitionofLiveBirth . . . . . . . . . . . . . . . . . . . . . . . . . ...47


SourcesofData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...47


NatalityStatistics . . . . . . . . . . . . . . . . . . . . . . . . . . . ...47


StandardCertificateofLiveBirth . . . . . . . . . . . . . . . . . . . . . 47


ClassificationofData . . . . . . . . . . . . . . . . . . . . . . . . . . ...49


AgeofMother . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...49


TotalBirthOrder . . . . . . . . . . . . . . . . . . . . . . . . . . . ...49

---

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CONTENTS–Con. 

Page 

Race and Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..49 

Place of Birth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

BirthWeight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...49 

PeriodofGestation . . . . . . . . . . . . . . . . . . . . . . . . . . ...49 

QualityofData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 

CompletenessofRegistration. . . . . . . . . . . . . . . . . . . . . ...50 

Quality Control Procedures . . . . . . . . . . . . . . . . . . . . . . ...50 

Sampling of Birth Records . . . . . . . . . . . . . . . . . . . . . . . ..51 

SYMBOLS 

Datanot available----------------------------------------

Category not applicable 

Quantity zero 

Quantity more than Obutless than 0.05-----

Figure does not meet standards of 

reliability or precision 

iv 

. . . 

-

0.0 

* 
TRENDS IN “PREMATURITY” 

UNITED STATES: 1950-67 

Helen C. Chase, Dr. P.H., National Academy of Sciences, 

and Mary E. Byrnes, M.A., Distn”ct of Columbia Department of Human Resourcesa 

INTRODUCTION 

In the United States infant mortality declined 

rapidly and at a fairly constant rate of decline 

for about the first half of the 20th century 

(figure 1). Around midcentury, the rate of 

decline decelerated and appeared to level off for 

about a decade.l Data for 1966-68 suggest a 

reassertion of a more rapid decline, but not at 

the pace experienced prior to 1950. 

When the data for the United States were 

compared with those for a group of economically and medically advanced Western European 

countries, it was found that the trends for some 

of the other countries seemed to be leveling off 

as well, but at considerably lower Ievels.z$3 For 

example, as recently as 1966, the infant mortality rate for the United States (23.7 per 1,000 

live births) was higher than the rate for Sweden 

(12.6), the Netherlands (14.7), and Australia 

(18.2 ).3 It also appeared that the proportion of 

infants weighing 2,500 grams (5% pounds) or 

less at birth (low birth weight infants) was 

higher among infants born alive in the United 

States than in Denmark, the Netherlands, 

Sweden, or New Zealand.3 Y4 Nationally, the 

percent of low birth weight among infants was 

reported to have been higher in 1960 than in 

January-March 1950, with practically no change 

for white infants but a marked increase for other 

infants.5 This observation, which was limited to 

a 3-month period in 1950 and to the year 1960, 

a Dr. Chase is Staff Associate (Blostatistics) at the Health 

Services Study, Institute of Medicine, National Academy of 

Sciences. Miss Bymes is Health Statistician, Community Health 

Services Adrnhdsttation, Dktrict of Columbia Department of 

Human Resources. At the time this study was completecL both 

authors were statisticians with the National Center for Health 

Statistics. 

10 ~ 

1915 1920 1930 1940 197C 

YEAR 

Figure 1. Infant mortality rates: United Statas, 1915-19 to 1967 

led to the present study, which covers the 

18-year period 1950-67. 

Among the many factors affecting infant 

survival, physical underdevelopment and immaturity at time of birth present the greatest 

hazards. In the United States, the risk of death 

in the first year of life among infants who weigh 

2,500 grams or less at birth is 17 times the risk 

among infants weighing 2,501 grams or more. 

1

Studies have shown that this ‘relative risk far 

exceeds the risk associated with disadvantageous 

birth order, sex, age of mother, or socioeconomic leveL6 Two national studies have 

shown that the risk differential associated with 

color (a ratio of 2:1, Negro and other minority 

races versus white) is considerably less than that 

associated with low birth weight (17: 1).5 ~7 

Not only are infants of low birth weight 

subject to a greater risk of death, but they are 

also subject to higher morbidity, particularly of 

the central nervous system.T’4s A greater prevalence of cerebral palsy, epilepsy, mental retardation, congenital anomalies, deafness, blindness, 

and strabismus has been found among infants of 

low birth weight and/or curtailed gestation than 

among fully developed full-term infants. None 

of these conditions is considered transient in 

nature; many of them are severe, and often they 

are chronic, as well as handicapping conditions. 

The data on associations between low birth 

weight and curtailed gestation on the one hand 

and excess mortality and morbidity on the other ,. requn-e further” clarification. For some of the 

conditions mentioned, low birth weight may be 

a consequence of the associated condition rather 

than a correlate of the causative mechanism. For 

example, an infant with severe congenital 

anomalies of the musculoskeletal system may be 

of low birth weight because the fetus was unable 

to grow to a fully developed infant after it was 

affected in utero.38 Such an infant may, nevertheless, be full term. On the other hand, other 

conditions may be resultants of low birth weight 

and/or curtailed gestation in the etiologic sense. 

In either case, birth weight and the duration of 

gestation together are assuming increasing importance, in evaluating the prognosis of newborn 

infants. 

In view of the serious nature of the disorders 

associated with low birth weight, public health is 

directing increasing attention to the causes and 

consequences of impaired fetal development. 

The evidence has been derived from a variety of 

studies, some retrospective, some prospective. If 

prematurity among newborn infants is truly 

increasing, then greater numbers of infants with 

severely handicapping conditions may be anticipated. 

Increasing proportions of infants of low birth 

weight have been reported in a study from one 

urban hospitals z Although an increasing trend 

was observed in this institution, it need not 

necessarily imply a nationwide trend. It may 

perhaps reflec{ a change in the composition of 

the hospital’s clientele or in the metropolitan 

population. Since the close of World War II, 

there have been large in-migrations of Negroes 

and other minority groups into large metropolitan centers, and at the same time there have 

been out-migrations of the more affluent white 

population to the suburbs. Because the proportion of low birth weight infants is higher among 

newborn infants of minority races, the rate in a 

single hospital or city is affected by the proportions of the two subgroups in the population 

studied. While the net effect of population 

changes over time may result in an increase in 

the proportion of low birth weight infants 

among those born in a specific hospital or city, 

the nationwide proportions must be considered 

separately. 

The present study explores the national data 

for the period 1950-67 and includes a critical 

review of the changes in the reporting of birth 

weight and gestation information. Trends by 

birth weight and gestational age are examined. 

The two variables are considered simultaneously 

for years for which published data are available. 

The proportion of low birth weight infants 

increased slightly from 7.5 percent in 1950 to 

8.2 percent in 1967. This was because the 

proportion among “other” infants increased 

markedly (from 10.2 percent to 13.6) while that 

among white infants remained relatively stable 

(around 7 percent). Using gestation data of less 

than satisfactory quality, a tentative conclusion 

was reached that there is no evidence of changes 

in gestation parallel to the changes in distributions of birth weight for “other” infants. Other 

factors such as age of mother, plurality, sex, and 

delivery in hospitals did not appear to explain 

the trends which were observed. 

Infants of low birth weight or those with 

curtailed periods of gestation are subject to 

much higher mortality and morbidity than their 

heavier counterparts, and their number is not 

inconsequential: 288,000 low birth weight 

infants were born in 1967 alone. Particularly 

prominent among “premature” infants are disorders of the central nervous system and congenitzd anomalies. Because of their severity and the 

2 
i 

long periods of treatment which may be 

required, the ultimate goal is not only the 

treatment of children born with these conditions 

but the prevention of the disorders and the 

prevention of “premature” birth. 

A complete assessment of prematurity should 

include all products of conception, i.e., fetal 

deaths as well as live births. The two groups of 

pregnancy terminations are interrelated, and 

changes which occur in the first group have an 

cf feet on the second. As an example, advances in 

the reduction of fetal deaths may affect the 

birth weight or gestational age distribution of 

live births. However, fetal death data for the 

United States include only those events of 20 

completed weeks or more of gestation, omitting 

about four-fifths of the fetal deaths which occur 

earlier in gestation. Even for fetal deaths of 20 

weeks or more of gestation, there is a high 

degree of underregistration (perhaps 20-25 

percent).4’4 In addition, a large proportion of 

fetal death records fail to indicate the birth 

weight or gestational age of the fetus, and these 

cannot be assumed to be unbiased. Because of 

these limitations of the fetal death data and 

because fetal deaths represent only 2-3 percent 

of pregnancies terminating at 20 completed 

weeks or more of gestation, it was decided to 

base this study on live births only. 

DEFINITIONS 

“Prematurity “ is a term which, in connection 

with newborn infants, is used generically to 

describe those who are not fully developed 

because of curtailed gestation, low birth weight, 

or both. During the period covered by this 

report, official as well as medical circles made a 

number of attempts to develop more quantitative descriptions of the term, 

In 1948 the First World Health Assembly of 

the World Health Organization (WHO) adopted 

the following definition, which was incorporated 

in the “International Statistical Classification of 

Diseases, Injuries, and Causes of Death”: 

For the purpose of this classification, an immature infant 

is a livebom infant with a bh-th weight of 5% pounds 

(2,500 grams) or less, or specified as immature. In some 

countries, however, this criterion will not be applicable. If 

weight is not specified, a livebom infant with a period of 

gestation of less than 37 weeks or specified as “premature” may be considered as the equiva!e~}of an immature 

infant for purposes of this efassification. 

In 1950, the WHO Expert Group on Prematurity reported as follows: 

The Expert Group on Prematurity recognizes the necessity 

for uniform terminology for intemationaf usage. Since the 

primary goal is to lower foetrd and neonatal mortality, this 

aim can best be achieved by providing speeifllzed care for 

infants of low birth-wei~t. ‘Ike group suggests that a 

premature infant be defined as one whose birth-weight is 

2,500 g. (5% pounds) or less. The limitations of this criterion 

are recognized, however, since data on bfi-weight will not 

always be available and other criteria of prematurity must be 

used, for example, gestation. The group there fore recommends the adoption by afl countries for purposes of vital 

statistics of the international definition of the First World 

Health Assembly . . . . 

The terms “immature” and “premature” are here used 

interchangeably. However, the group points out that the term 

“premature” is preferable to the term “immature’’.46 

It should be noted that this definition differs 

from the earlier statement. It states that a 

premature infant be defined as one whose birth 

weight is 2,500 grams (5% pounds) or less, and 

although “premature” and “immature” are used 

interchangeably, the term “Prema~re” is 

preferred. 

In 1961, the WHO Expert Committee on 

Maternal and Child Health noted that the 

definition of prematurity (birth weight of 2,500 

grams or less) recommended by the WHO Expert 

Group on Prematurity “has been adopted almost 

universally and has proved very helpful in many 

parts of the world, especially is assessingthe size 

of the problem. ”A 7 The Committee further 

pointed out: 

There is in realky no sharp dividing line between mature and 

premature babies or between high and low birth 

weight. . . . In view of the convincing evidence showing that 

many of the babies included within tbe limits of the 

definition, in certain areas, are not born prematurely, the 

Committee recommends that the concept of $’prematurity” 

in the definition should give way to that of “low birth 

weight.’*7 

The definition of “low birth weight” as 2,500 

grams or less has been criticized for its lack of 

universalisty. Although infants who weigh 2,500 

grams or less at birth maybe considered to.be of 

low birth weight and are often preterm in the 

United States, in other countries a high proportion of them may be full term, but of small 

stature. 

3 
Within the United States, the international 

definitions proposed by WHO in 1950 found 

general acceptance in official and medical 

circles. For a number of years, the term “premature” was widely used for infants who weigh 

2,500 warns or less at birth. However, with 

increased knowledge, there developed an uneasiness in medical circles about this particular 

definition of prematurity, and a number of 

professional organizations made independent 

attempts to revise it during the 1960’s. Committees of the American Medical Association,4 8,4 g 

the American College of Obstetricians and 

Gynecologists, 50,5 I md the American Academy 

of PediatricsZY58 have drafted definitions of 

terms relating to various aspects of prematurity. 

They have recognized the problems caused by 

the lack of uniformity, but as yet have not 

arrived at a common set of definitions. 

A number of studies have indicated that 

infant survival and morbidity are affected by 

both gestation and birth weight, and independent investigations have also attempted to 

create new classifications” encompassing both 

variables.G4-b8 Once again, there is a lack of 

uniformity among them, both with regard to 

the statistical methods for determining classes 

and with regard to group limits. 

Presently, it is generally agreed that words 

such as “premature” and “immature” as designations of quantitative classifications should be 

avoided. The tentative resolution of this problem has been the recommendations that both 

measures of maturity (gestational age and birth 

weight) should be expressed quantitatively 

rather than qualitatively and that precise quantitative terms should be used to avoid misunderstanding. At first glance, this appears to be a 

rational solution, and it simplifies the problem 

of classification and tabular presentation for 

statisticians. However, when these recommendations are strictly adhered to, the language 

becomes extremely convoluted and is difficult 

to follow. Therefore, in this report, certain 

patterns of language have been adopted for the 

sake of clarity and simplicity. 

In this report, “prernatur~ty“ is sparingly used 

in its generic sense, i.e., a “premature” infant is 

one who is not fully developed because of 

curtailed gestation, low birth weight, or both. 

Infants who are premature because of curtailed gestation (gestational age of less than 37 

completed weeks) are designated “preterrn.” 

Registration areas in which gestational age is 

determined by computation from the date of 

the first day of the last normal menstrual period 

(LMP) to the date of birth are termed “areas 

reporting LMP.” All other areas are termed 

“areas reporting weeks of gestation.” 

Infants who are premature by virtue of birth 

weight (2,500 grams or less at birth) are designated “low birth weight” infants. 

These conventions are used for the purpose of 

this report and are not to be considered official 

terminology. 

SOURCE OF DATA 

The data for the present report are taken 

from Vital Statistics of the United States for the 

years 1950 through 1967 and are based on live 

births which occurred and were registered in the 

United States. The registration of vital events is 

conduct ed by the States in accord with State 

statutes. Forms for registering live births are 

designed and printed by the individual States, 

but they are usually patterned after the Standard Certificate of Live Birth recommended by 

the Surgeon General of the Public Health Service. Even in States where the exact format of the 

standard certificate is not used, the content of 

the record closely follows the standard certificate. Because State statutes are enacted at 

different points in time and because final decisions regarding the design of the certificates rest 

with the States, it is not always possible to have 

complete uniformity in national data for all 

items. Some States require more items of information to be recorded than others, and the 

structure of an individual item may vary from 

one State to another. The question regarding the 

period of gestation may request “weeks of 

gestation,” or it may request “first day, last 

normal menstrual period.” Responses to these 

two questions yield quite different statistical 

distributions. Although the national data contain a number of such interstate variations, it is 

important to emphasize that there is a high 

degree of uniformity in the live birth records 

that emanate from the State vital records 

systems. 

In the present report, analysis of trends in 

prematurity will depend primarily on two items 

4 
of information from the live birth records, i.e., 

birth weight and period of gestation. These two 

characteristics will first be considered separately, 

and later simultaneously. 

During the interval 1950-67, two revisions of 

the Standard Certificate of Live Birth were 

used. The 1949 revision of the Standard Certificate of Live Birth requested the length of 

pregnancy (weeks) and the weight at birth (lb., 

oz.). In the 1956 revision, the item on birth 

weight remained unchanged, and the gestation 

item was refined to ask for “completed weeks. ” 

The reporting of birth weight was required on 

the live birth certificates of all States except 

Massachusetts and Connecticut in 1950 (Technical Appendix). By 1957, Massachusetts was the 

only State which did not include birth weight on 

its live birth certificates, and by 1959 the 

inclusion of this item was nationwide. Similarly, 

for period of gestation, the number of States 

requiring the reporting of this item has not 

provided nationwide coverage for this entire 

period. The Technical Appendix includes a list 

of the States which, according to Vital Statistics 

of the United States, did not require gestation 

information on live birth records. As recently as 

1967, live birth record forms used in the State 

of Massachusetts and that part of Maryland 

outside the city of Baltimore did not include an 

item requesting period of gestation. 

COMPLETENESS OF DATA 

Each year, some live births are registered for 

which the birth weight or the period of gestation, although required on the birth certificate, 

is not stated. The percentage has changed over 

the years, but it is not large enough to affect the 

distributions to any marked degree: 

Birth

Year Gestation 

weight 

I 

Percent with item 

not completed 

1950 . . . . . . . . . . . . . . . . . . . 12.7 23.4 

1967, . . . . . . . . . . . . . . . . . . 0.2 33,6 

‘ Excludes data for Connecticut and Massachusetts, 

2 Excludes data for Louisiana and Massachusetts. 

‘ Excludes data for Massachusetts and Maryland, outside 

Baltimore. 

The data which are excluded are for States 

which did not request birth weight and/or 

gestational age on their live birth records. These 

data would have covered the entire weight or 

gestational range; and since they were a small 

portion of the total, they could not affect 

percentage distributions for the entire United 

States to any marked degree. The proportion of 

live birth records with birth weight or gestational age unspecified for the remaining States 

were felt to be small enough so that the 

omission of these records would not affect the 

national distributions. Therefore, for the present 

study of live births, the data are based on 

records with stated birth weight and gestational 

age, and it is assumed that the omissions which 

have been noted will not seriously affect the 

distributions which are shown. 

ACCURACY OF DATA 

Several factors contribute to inaccuracies in 

the data for period of gestation. First, “gestational age” is only an estimate of the true period 

of gestation. The true period of gestation is 

defined as the time from conception to birth. 

Because the exact time of conception cannot be 

determined, gestational age is used as an indicator of gestation. Gestational age is measured 

from the onset of the last menstrual period 

(LMP) to the date of birth. It is generally agreed 

that, on the average, conception occurs about 2 

weeks after the onset of the LMP. This discrepancy of 2 weeks is recognized by medical 

authorities and is described in standard textbooks of obstetrics. 

Second, accurate recording of gestational age 

is also dependent on the mother’s ability to 

recall the date of the onset of the LMP and to 

furnish the information to her physician or to 

the hospital staff. This element of recall 

undoubtedly introduces some error into the 

recorded information. Further inaccuracies in 

gestational age maybe introduced by the doctor 

or other hospital personnel when the onset of 

the LMP is entered in the hospital record, when 

the gestational age is calculated from the dates 

which are given, or when the information is 

transposed to the birth certificate. 

As an illustration of the differences incurred 

by the two methods of recording gestational age, 

the distributions of live births by completed 

5 
weeks of gestation are shown for New York 

State in table A. The data are presented separately for New York City, where the official 

record requested the first day, LMP, and for the 

rest of the State, where the record requested 

completed weeks of gestation. The data demonstrate a higher proportion of records with 

gestation not stated when the item requests LMP 

(2.3 percent) than when the record requests 

weeks of gestation (less than 0.05 percent). A 

much larger discrepancy is evident in the percentage distributions in the category of 40 

weeks and over; in New York City (area reporting LMP), the proportion in this group is 44.8 

percent, while in the rest of the State (area 

reporting weeks of gestation) it is almost 

doubled (80.3 percent). The magnitude of this 

difference is largely offset in the preceding 

group, 37-39 weeks, where the percentage for 

the area reporting LMP is 41.2 percent, while 

that for the area reporting weeks of gestation is 

14.1 percent. In addition, the patterns in the 

groups under 37 weeks differ. In the area 

reporting LMP, there is a gradual increase in the 

percentages between 31 weeks and 36 weeks, 

while in the area reporting weeks of gestation, 

there is a suggestion of clusters at 32 and 36 

weeks in addition to the large cluster in the 

group “40 weeks and over” that has already 

been mentioned. Differences of this kind and 

size could not be due to real differences in 

gestational age. 

Although one cannot categorically conclude 

from these data that gestational age computed 

from the onset of the last menstrual period is 

perfect, the resulting distribution is far more 

rational, and in that sense it is considered an 

improvement over the data based on reported 

weeks of gestation. The LMP date has also been 

demonstrated to be an acceptable item of 

information when compared to currently maintained menstrual histories.59 

By 1967, only a few of the registration areas 

in the United States could tabulate period of 

Table A. Number of recorded live births and percentage distribution by period of gestation: New York City and rest 

of New York State, 1960 

Period of gestation 

Total . . . . . . . . . . . . . . . . . . . . . 

Lessthan20weeks . . . . . . . . . . . . . . . . . 

20-25 weeks . . . . . . . . . . . . . . . . . . . . . 

26-27 weeks . . . . . . . . . . . . . . . . . . . . . 

28-29 weeks . . . . . . . . . . . . . . . . . . . . . 

30weeks . . . . . . . . . . . . . . . . . . . . . . . 

31 weeks . . . . . . . . . . . . . . . . . . . . . . . 

32 weeks . . . . . . . . . . . . . . . . . . . . . . . 

33weeks . . . . . . . . . . . . . . . . . . . . . . . 

34weeks . . . . . . . . . . . . . . . . . . . . . . . 

35weeks . . . . . . . . . . . . . . . . . . . . . . . 

36weeks . . . . . . . . . . . . . . . . . . . . . . . 

37-39 weeks, ,,, . .,.,...,, . . . . . . . 

40weeks and over . . . . . . . . . . . . . . . . . . 

Notstated . . . . . . . . . . . . . . . . . . . . . . 

New York Rest of New New York I

Rest of New 

Cityl York State2 Cityl York State2 

Number of live births Percentage distribution 

166,300 194,915 100.0 100.0 

182 38 0.1 0.0 

815 746 0.5 0.4 

544 348 0.3 0.2 

823 558 0.5 0.3 

693 505 0.4 0.3 

828 251 0.5 0.1 

1,172 ’955 0.7 0.5 

1,714 452 1.0 0.2 

2,564 1,083 1.5 0.6 

3,880 1,103 2.3 0.6 

6,291 4,938 3.8 2.5 

68,563 27,445 41,2 14,1 

74,471 156,421 44.8 80.3 

3,760 72 2.3 0.0 

1Gestation is ~omput~ from LMp date and date of birth as they are recorded on birth certificate.


‘Gestation is recorded in weeks at point of origin of birth certificate.


Source: State of New York Department of Health: Eighty-first Annual Statistical Report for the year ending Dacember 31, 1960.


6 
I


gestation derived from the LMP date. In that 

year, data based on the LMP date were available 

from the live birth certificates of only five 

registration areas: Baltimore, California, District 

of Columbia, Minnesota, and New York City. 

For the rest of the country, gestational age was 

based on weeks of gestation as recorded on the 

live birth certificates. 

Because of the heapings at certain weeks of 

gestation, the categories of period of gestation 

shown in Vital Statistics of the Waited States are 

not uniformly divided. The categories for which 

data are published are as follows: 

Under 20 weeks 

20-27 weeks 

28-31 weeks 

32-35 weeks 

36 weeks 

37-39 weeks 

40 weeks 

41-42 weeks 

43 weeks and over 

Not stated 

Data which are categorized in this detail call 

attention to the heapings at 36 and 40 weeks. 

Figure 2 shows the gross distortions which are 

introduced into the national data when gestational age is reported in weeks of gestation on 

the birth records. The distribution of live births 

by gestation as derived for areas reporting LMP 

is used as the tentative standard to which other 

data are compared. While the gestational ages 

derived from LMP dates cannot be assumed to 

be error free, they are the best which are 

currently available for vital statistics data. The 

number of live births with gestation periods of 

less than 37 weeks are understated in the relative 

sense by about 37 percent. At 37-39 weeks, 

there is about a 64-percent understatement, at 

40 weeks about a 222-percent overstatement, 

and about a 77-percent understatement in the 

gestation interval of 41 weeks and over. Apparently, when weeks of gestation are recorded on 

the birth records, a great number of births are 

automatically recorded as having periods of 

gestation of 40 weeks instead of the actual 

periods of gestation as calculated from the onset 

of the last menstrual period. 

The magnitude of the error becomes even 

more disturbing when it is recognized that 98 

percent of live births occur in hospitals or are 

6.6 

L 

Under 28-31 32.35 36 37-39 40 41-42 43 and 

28 over 

WEEKSOF GESTATION 

Figure 2. Percentage distribution of live births by period of gestation: Areas reporting LMP and areas reporting weeks of 

gestation, 1967. 

attended by physicians in clinics. Theoretically, 

the best possible information should be available 

from these sources. In spite of the almost 

universal practice of delivery in hospitals in the 

late 1960’s, gestational age in ~weeks was not 

considered to be accurately recorded on the live 

birth records covering the greater part of the 

United States. The situation may improve considerably beginning with data for 1968 due to 

the introduction of revised birth certificate 

forms by many of the States in that year. 

The recording of gestational age is also subject 

to errors of recall. It requires the mother to 

remember and transmit to her physician the 

information relating to the onset of the last 

menstrual period. If she is under prenatzd care 

and provides her physician with this information, it is also necessary that the LMP date (or 

weeks of gestation) be transmitted from the 

7 

0.8 
physician’s office to the hospital where the birth 

will occur and where the certificate will be 

prepared. If either of these links in the chain of 

events is broken, there is a temptation on the 

part of hospital staff to second-guess the information. If weight at birth is 5% pounds or more, 

the infant is often assumed to be full term and is 

recorded as having a gestational age of 40 weeks. 

This presumptive procedure has been described 

in a number of personal discussions with hospital personnel and, unfortunately, is said to be 

rather widespread. The magnitude of the effect 

on the statistical data is unknown, but from the 

degree of the statistical heaping at 40 weeks it is 

assumed to be serious. 

Birth weight, on the other hand, is measured 

on hospital scales at time of birth for the large 

majority of infants who are born in hospitals. It 

is a more objective measure because it avoids the 

biases of maternal recall, and it does not depend 

on the transmittal of information from prenatal 

records in physicians’ offices to hospital records, 

For infants born in hospitals, where scales are 

usually available and easily accessible, the 

recording of birth weight is probably more 

reliable and more complete than the recording 

of gestation. 

For some of the years included in this report, 

the data for live births are based on samples 

(Technical Appendix). For the years 1951 to 

1954 and 1956 to 1966, inclusive, the data are 

based on 50-percent systematic samples of live 

birth certificates. For the year 1967, the data 

are based on a 20- to 50-percent sample. All 

other years represent complete counts. Despite 

the limitations due to sampling, the data are 

acceptable for identifying major trends, although minor changes cannot be identified with 

confidence. 

FINDINGS


The number of live births in the United States 

increased from about 3.6 million in 1950 to 4.3 

million in 1957 (table 1). After a small decrease 

in 1958, the number increased again, reaching a 

peak of 4.3 million in 1961. Since then, there 

has been a steady decline until, in 1967, the 

number of live births (3.5 million) was about the 

same as it was in 1950. Of the 3.5 million live 

births in 1967, 2.9 million (83 percent) were 

white, and 600 thousand (17 percent) were 

infants of other races. 

PERIOD OF GESTATION 

Trends 

The number of live births and percentage 

distributions of live births by period of gestation 

for white and for all other infants over the 

period 1950-67 are shown in tables 1 and 2, 

respectively. The large frequencies in the “Not 

stated” category in table 1 are due to the 

omission of a question regarding gestational age 

from the official record forms of certain States. 

When the live births which occurred in these 

States are omitted, the percent of records with 

gestation unspecified was relatively small: 3.4 

percent in 1950 and 3.6 percent in 1967. The 

percentages shown in table 2 are based on 

records with stated gestational ages. The percentages are shown first for live births with 

gestational age under 37 weeks and those 37 

weeks and over, the dividing point recommended by the World HeaIth Organization for 

classifying infants into preterm and full-term 

deliveries. 

For all births, there appears to be some 

decline in the proportion of live births which 

were classified as preterm in the first few years 

of the 18-year period. In recent years, particularly since 1965, the proportion seems to have 

stabilized. However, this decline has almost 

completely paralleled the decline in the 36-week 

group alone; in fact, the difference between the 

percentages in 1950 and those in 1967 are very 

close: 4.4 percent for all births and 4.7 percent 

for 36 weeks (table B). There is a remarkable 

consistency in the proportions in the two 

shortest gestation periods (less than 28 weeks, 

and 28-31 weeks). The most notable changes in 

the distributions by gestation which are shown 

in table 2 are the decreases over time in the 

gestation periods of 36 weeks and 40 weeks (or 

40 weeks and over) and the increases in all other 

periods. The directions of change are opposite in 

8 
Table B. Percentage distribution of live births by gestation and color: United States, 1950 and 1967 

Period of gestation k 

19501 

Total . . . . . . . . . . . 100.0 

P 

Under 37weeks . , , . . , 11.1 

37waeks and over . . . . . 88.9 

Under 28weeke . . . . , . . . . 0.6 

28-31 weeks ., ...,,.... 0.9 

32-35 weeks . . . . . . . . . . . 2.0 

36weeks . . . . . . . . . . . . . 7.6 

37-39 walks . . . . . . . . . . . 8.5 

40weaks . . . . . . . . . . . . . 76.9 

41-42 weeks . . . . . . . . . . . 3.0 

43weeksand over , . . . . . . . 0.4 

Total White 

19672 Difference 19501 19672 Difference 19501 

100.0 . . . 100.0 100.0 . . . 100.0 — 

6.7 -4.4 10.4 5.9 -4.5 15.9 

93.3 +4.4 89.6 94.1 +4.5 84.1 

0.6 0.5 0.5 0.8 

0.8 -0.1 0.8 0.7 -0.1 1.4 

2.5 +0.5 2.0 2.2 +0.2 2.1 

2.9 -4.7 7.0 2.6 -4.4 11.5 

17.5 +9.0 8.8 17.6 +8.8 6.7 

65.7 -11.3 77.1 65.6 -11.5 75.9 

8.4 +5.4 3.3 9.2 +5.9 1,3 

1.7 +1.3 0.4 1.7 +1.3 0.3 

All other 

19672 Difference 

100.0 . . . 

11.0 -4.9 

89.0 +4.9 

1.1 +().3 

1.6 +0.2 

3.9 +1.8 

4.4 -7.1 

16.9 +1 0.2 

66,1 -9.8 

4.7 +3.4 

1.3 +1.0 

1Excludes all live births recorded in Louisiana and Massachusetts.


‘ Excludes all live births recorded in Massachusettsand Maryland outside 8altimore.


adjacent gestation categories: a small increase in 

the group 32-35 weeks (2.0 to 2.5 percent), a 

decrease at 36 weeks (7.6 to 2.9 percent), a 

doubling at 37-39 weeks (8.5 to 17.5 percent), 

another decrease at 40 weeks (76.9 to 65.7 

percent), and increases at 41-42 weeks (3.0 to 

8.4 percent) and 43 weeks and over (0.4 to 1.7 

percent). 

The alternating increases and decreases lend 

credence to the hypothesis that the changes may 

be due to more accurate determination of weeks 

of gestation rather than a true change in 

gestation among live births. The increased accuracy may be attributed to two factors: introduction of the LMP item on the records in some 

parts of the United States and perhaps increased 

care in computing the weeks of gestation in 

other areas. 

During the period 1950-67, two methods of 

deriving gestat{onal age were used in the United 

States. The introduction of the new item 

requesting “first day, last menstrual period” 

rsxult cd in a markedly different distribution of 

live births by period of gestation. The concentrations at single weeks which are multiples of 4 are 

markedly reduced, and there is a greater dispersion among the intermediate weeks of gestation 

(table C). The number of areas reporting LMP 

was never very large during the period covered 

by this report; live births in these areas accounted fo~ only 17.1 percent of all live births 

in the United States in 1967. 

A second possible factor affecting the distribution of live births by gestation is the scattered 

and sporadic attempts in a number of States to 

encourage physicians and hospitals to record 

weeks of gestation with greater accuracy when 

the question on the record is phrased in such 

terms. By comparing the 1950 dktribution when 

none of the data were based on LMP and the 

distribution of areas reporting weeks of gestation in 1967, it is apparent that there were 

relatively minor changes in the distribution of 

gestational ages due to this factor (table D). The 

single group with the greatest frequency (40 

weeks) decreased from 76.9 to 73.5 percent, 

which is still far from the 22.8 percent which 

was found when the onset of the LMP was 

reported (table C). Important relative changes 

were the decrease at 36 weeks (7.6 to 2.8 

percent) and the increase at 37-39 weeks (8.5 

to 13.7 percent). A greater part of the decrease 

at 36 weeks seems to be related to the increase 

in the lonqer gestation at 37-39 weeks rather 

than to ~he }eriod of 32-35 weeks which 

appeared unchanged. Rather significantly, there 

was no major change in the three shorter 

gestation groups: only in the group representing 

9 
Table C. Number of live births end parcentega distribution by period of gestation and color for areas reporting LMP and othar araas: 

United States, 1987 

Period of gestation 

and color 

Total . . . . . . . . . . . . . . . . . . . . 

Under 28weaks . . . . . . . . . . . . . . . . . 

26-31 weeks . . . . . . . . . . . . . . . . . . . 

32-35 weeks . . . . . . . . . . . . . . . . . . . 

36weeks . . . . . . . . . . . . . . . . . . . . . 

37-39weeks . . . . . . . . . . . . . . . . . . . 

40weeks . . . . . . . . . . . . . . . . . . . . . 

4142weeks . . . . . . . . . . . . . . . . . . . 

43weaksandover . . . . . . . . . . . . . . . . 

Notstatad . . . . . . . . . . . . . . . . . . . . 

White . . . . . . . . . . . . . . . . . . . 

Under28weeks . . . . . . . . . . . . . . . . . 

28-31weeks . . . . . . . . . . . . . . . . ... . 

32-35weeks . . . . . . . . . . . . . . . . . . . 

36weeks . . . . . . . . . . . . . . . . . . . . . 

37-39weeks . . . . . . . . . . . . . . . . . . . 

40weaks . . . . . . . . . . . . . . . . . . . . . 

41-42weeks . . . . . . . . . . . . . . . .. . . . 

43weeksandover . . . . . . . . . . . . . . . . 

Notstated . . . . . . . . . . . . . . . . . . . . 

Another . . . . . . . . . . . . . . . . . . 

Uncier28weeks . . . . . . . . . . . . . . . . . 

28-31 weeks . . . . . . . . . . . . . . . . . . . 

32-35weeks . . . . . . . . . . . . . . . . . . . 

36weeks . . . . . . . . . . . . . . . . . . . . . 

37-39weeks . . . . . . . . . . . . . . . . . . . . 

40waeks . . . . . . . . . . . . . . . . . . . . . 

41-42weeks . . . . . . . . . . . . . . . . . . . 

43weaksandover . . . . . . . . . . . . . . . . 

Notstatad . . . . . . . . . . . . . . . . . . . . 

Areas Areas reporting Total reporting gestation LMP1 period 

I 

Number 

3,520,859 601,337 2,919,622 

18,956 3,660 15,296 

26,478 5,687 20,791 

80,837 24J21 56,516 

93,821 16,680 77,141 

571,062 193,600 377,462 

2,142S88 114,639 2,028,349 

274,739 111,599 163,140 

54,217 33,102 21,115 

257,861 98,049 159,812 

2,922,502 492,633 2,429,669 

12,476 2,153 10)323 

17,625 3,626 13,999 

59,102 16992 42,110 

69,021 12,333 56,688 

475,721 156,564 319,157 

1,770,029 97/632 1,672,197 

248,291 97,030 151,261 

46,760 27,575 19,185 

223,477 78,528 144949 

598,457 108,704 489,753 

6,480 1,507 4,973 

8,853 2,061 6,792 

21,735 7,329 14,406 

24,800 4,347 20,453 

95,341 37036 58,305 

372,959 16fi07 356,152 

26,448 14,569 11 B79 

7,457 5,527 1,930 

34,384 19,521 14,863 

Areas Areas 

Total reporting raporting 

LMP1 gastetion 

period 

Percentage distribution 

100.0 100.0 100.0 

0.6 0.7 Y 

0.8 1.1 0.8 

2.5 4.8 2,0 

2.9 3.3 2.8 

17.5 38.5 13.7 

65.7 22.8 73.5 

8.4 22.2 5,9 

1.7 6.6 0.8 

. . . . . . . . . 

100.0 100.0 100.O 

0.5 0.5 0.5 

0.7 0.9 0.6 

2.2 4.1 1.8 

2.6 3.0 2.5 

17.6 37.8 14.0 

65.6 23.6 73.2 

9.2 23.4 6.6 

1.7 6.7 0.8 

. . . . . . . . . 

100.0 100.0 100.0 

1.1 1.7 1.0 

1.6 2.3 1.4 

3.9 8.2 3.0 

4.4 4.9 4.3 

16.9 41.5 12,3 

66.1 16,8 75.0 

4,7 16.3 2.5 

1.3 6.2 0,4 

. . . . . . . . . 

‘Fiaures bv Deriod of gestation for these areas are based on an item on the birth record—first day of Iast normal menstrual period 

(LMP)~ Areas ~ncludad are-Baltimor% California, District of Columbia, 

Negroes and other minority races, at 32-35 

weeks, was there asuggestion ofanincreaee (2.1 

to 3.0 percent). The improvement in reporting 

weeks of gestation between 1950 and 1967 is 

minor compared to the change which resulted 

from the introduction of the LMP date on the 

record forms in some States. 

In summary, the changes in the distributions 

by period of gestation do not suggest that there 

was an increase in the incidence ofpreterm live 

birthsbetween 1950 and 1967.Thefact that the 

Minnesota and New York City. 

early gestations (less than 36 weeks) were 

virtually unaffected lends further support to this 

view. On the contrary, it would seem that a 

great part, ifnot all, of the changes which were 

noted may well be associated with artifacts in 

the reportingof the data. 

Color 

When groups of infants are compared by 

color, one finds higher proportions of preterm 

10 
Table D. Percentage distribution of Iivebirths bycolorand period of gestation: United Statesr 1950, andareas notrepotiing LMP, 

1967 

* 

Total White All other 

Areas Areas Areas 

Period of gestation reporting reporting reporting 

19501 gestation 19501 gestation 19501 gestation 

period period period 

19672 19672 19672 

Total . . . . . . . . . . . . . . . 100.0 100.0 100.0 100.0 100.0 

Under 28weeks . . . . . . . . . . . . . 0.6 0.6 0.5 0.5 0.8 

28-31 weaks . . . . . . . . . . . . . . . 0.9 0.8 0.8 0.6 1.4 

32-35 weeks . . . . . . . . . . . . . . . 2.0 2.0 2.0 1.8 2.1 

36weaks . . . . . . . . . . . . . . . . 7.6 2.8 7.0 2.5 11.5 

37-39waeks . . . . . . . . . . . . . . . 8.5 13.7 8.8 14.0 6.7 

40weeks . . . . . . . . . . . . . . . . 76.9 73.5 77.1 73.2 75.9 

4142waaks . . . . . . . . . . . . . . . 3.0 5.9 3.3 6.6 1.3 

43waaksendover, . . . . . . . . . . . 0.4 0.8 0.4 0.8 0.3 

‘Excludes Louisiana and Massachusetts. 

100.0 

1.0 

1.4 

3.0 

4.3 

12.3 

75.0 

2.5 

0.4 

‘Excludes Massachusetts and Maryland outside Baltimore. The following are LMPareas andaretherefore also excluded: Baltimora.-. District of Columbia, Minnesota and New York City. 

infants (less than 37 weeks) among Negroes and 

other minority infants than among the white 

infants. This relationship is evident throughout 

the period 1950-67 (table 2) and when the areas 

reporting LMP are shown separately (table C). In 

the early gestations (less than 36 weeks), there is 

the suggestion of a small increase in the proportions for Negroes and other minority infants, 

while proportions for white infants remain 

relatively unchanged (table 2). The number of 

live births included in these short gestational 

ages is a small proportion of the live births for 

each group. 

Future Prospects 

The Standard Certificates of Live Birth and 

Fetal Death were revised and recommended to 

the States for introduction beginning in 1968. 

On this revision, the question regarding gestation 

was changed to ask for the first day of the last 

menstrual period. Virtually all of the States have 

adopted the new form of live birth certificate 

and, as a consequence, it is hoped that within a 

few years more reasonable distributions of live 

births by gestation will be available. There will, 

inevitably, be a few years of accommodation 

during which physicians and hospital staffs will 

need to become accustomed to the new question. This may require the closer coordination of 

this item of information between physicians’ 

offices and hospital record rooms. Recording the 

new information with greater accuracy and with 

a reasonable degree of completeness should 

make the data by period of gestation much more 

useful in considering perinatal problems. As was 

noted earlier, the gestation information, when 

reported in weeks, showed almost no improvement over the 18-year period included in this 

report. The change to the LMP form of inquiry 

was, therefore, not wdertaken in haste, but 

only after serious consideration of the persistent 

distortions of the recorded information over a 

long period of time. 

WEIGHT AT BIRTH 

Trends 

The number of live births and percentage 

distribution of live births by birth weight and 

color are shown for the period 1950-67 in tables 

3 and 4, respectively. The large numbers of 

records with birth weight not stated consist 

mostly of births in States which did not have a 

11

birth weight item on their live birth records 

(table 3). If these States are excluded, the 

percent of records with birth weight unspecified 

is small and has decreased: 2.7 percent in 1950 

and 0.2 percent in 1967. Therefore, the percentages shown in table 4 are based on records 

with specified weight at birth. 

The distribution of birth weight for all births 

has shown a remarkable degree of regularity 

during the period 1950-67, reflecting the relatively stable trend for white infants (table 4). 

For all births, the proportion weighing 2,500 

grams or less at birth increased slowly from 7.5 

percent in 1950 to 8.3 percent in 1965 and 

1966. For 1967 it was only slightly less, 8.2 

percent. For the year 1967 alone, this represented about 288,000 live born infants who, by 

definition, are low birth weight infants. 

The proportion of low birth weight among 

white infants varied only from 6.7 to 7.2 

percent in the study period (table 4 and figure 

3). In the most recent 5 years which are shown 

15 

**.***,*.*“’’’*’” “’’”%, 

**.**’.tI,,,,,,,,,,,,ssa* J*”” 

,,,,. ,,,,,. **,**, All other 

**,.,.***’” l~@ *,** ,,,. 

. 

10 

1-

Z 

w 

c1 

c 

w 

L 

White 

5 

0 I I 1 I I I I I 1 I t 1 t 1 1 I I 

1950 1955 1960 1965 

YEAR 

Figure 3. Percent of live births with low birth weight by color: 

United States, 1950-67. 

(1963-67), the rates were either 7.1 or 7.2 

percent. Although these are higher than the 

previous 5 years (1958-62), the rates in the first 

5 years (1950-54) were almost equally high. For 

white infants, therefore, there is no evidence of 

any marked increase or prolonged increasing 

trend in the proportion of low birth weight 

infants: it was roughly 7 percent throughout this 

entire period. 

The data for other infants differ in two 

respects. First, even in the earliest year shown 

(1950), the proportion weighing 2,500 grams or 

less at birth (10.2 percent) was significantly 

higher than that of white infants (7.1 percent), 

and it remained consistently higher through the 

18-year period. Second, the difference between 

the two color groups has increased progressively. 

By 1967, when the proportion of low birth 

weights among white infants was the same as in 

1950 (7. 1 percent), the proportion for other 

infants was 13.6 percent compared with 10.2 

percent in 1950. The annual figures showed a 

generally increasing trend for other than white 

infants over the period 1950-67 in contrast with 

the relatively unchanging proportions for white 

infants (fig. 3). 

There are no offsetting or systematic increases 

and decreases between adjacent groups in the 

birth weight distributions for total, white, or 

other infants (table E). For the last group, it 

appears that there has been a shift of the entire 

birth weight distribution toward lower birth 

weights between 1950 and 1967. The shift 

results from rather regular decreases in each of 

the birth weight groups over 3,500 grams, with 

all of the counterbalancing increases in groups 

up through 3,500 grams. No corresponding shift 

is found in the distribution for white infants. 

There has been a marked decrease in the 

number of records with birth weight unspecified 

for each color group. However, the greater part 

of the decline has resulted from an increase in 

the number of States including the birth weight 

item on their records. This development could 

have had relatively little effect on the national 

distribution since, for each State, the live births 

cover the complete range of birth weight. Once 

the data for these States were omitted, the 

proportions of certificates with birth weight 

unspecified were low, and their gradual decline 

is not of sufficient magnitude to account for the 

12 
Table E. Percentage distribution of live births by birth weight and color: United States, 1950 and 1967 

Birth weight 

Total . . . . . . . . . . . 

2,500 grams or less . . . . . . 

2,501 grams or more . . . . . 

1,000 grams orless . . . . , . . . 

1,001 -l,500grams . . . . . . . . 

1,501-2,000 grams . . . . . . . . 

2,001-2,500 grams , . . . , . . . 

2,501-3,000 grams , . . . . . . . 

3,001-3,500 grams . . , , . . . . 

3,501-4,000 grams . . . . . . . . 

4,001-4,500 grams . . . . . . . . 

4,501 grams or mora . . . . . . . 

Total White All other 

19501 1967 Difference I9501 1967 Difference 19501 1967 >ifference 

100.0 100.0 100.0 100,0 100.0 100.0 . . . 

7.5 8.2 +0.7 7.1 7.1 10.2 13.6 +3.4 

92.5 91.8 -0.7 92.9 92.9 89.8 86.4 -3.4 

0.4 0.5 +().1 0.4 0.4 0.6 1.1 +0.5 

0.6 0.7 +0.1 0.6 0.6 “0.9 1.2 +0.3 

1.4 1.6 +().2 1,3 1.3 2.0 2.7 +0.7 

5.1 5.4 +0.3 4,8 4.8 6.8 8.6 +1.8 

18.3 19.7 +1.4 17.8 18.3 +0.5 21.4 26.4 +5.0 

37.9 38.5 +0.6 38.3 38.7 +’0.4 35.4 37.5 +2.1 

26.9 25.5 -1.4 27.5 27.1 -0.4 22.8 17.8 -5.0 

7.5 6.7 -0.8 7.6 7.3 -0.3 6.9 3.8 -3.1 

1,9 1.3 -0.6 1.7 1.4 -0.3 3.3 0.9 -2.4 

i Excludes all live births recorded in Connecticut and Massachusetts. 

shift in the entire national distribution of weight 

at birth for other than white infants. 

In summary, therefore, one may conclude 

that the incidence of low birth weight has been 

higher among other infants than among white 

infants throughout the period 1950-67. Furthermore, the difference between the two groups has 

been generally increasing over this period. 

Future Prospects 

It is generally agreed that weight at birth is a 

more complete and more accurate item than 

gestational age. Birth weight, too, presents problems, but of a different nature. Birth weight is 

recorded on the vast majority of live birth 

records in pounds and ounces. To facilitate 

comparisons with medical data and with data for 

other countries where the metric system is used, 

birth weight is converted from pounds and 

ounces to grams and classified in 500-gram 

groups for - publication. The equivalent= in 

pounds and ounces and gram intervals are given 

in the Technical Appendix. The distribution of 

live births over these weight classes is not 

uniform: over 80 percent of live born infants 

weigh between 5 pounds 9 ounces and 8 

pounds 13 ounces (2,501-4,000 grams) as 

shown in table E. The customary classes of 500 

grams would seem to be too broad for a 

characteristic of small variation, and finer classes 

of 250 grams (or perhaps even 100 grams for the 

predominant weight groups) have been 

suggested. 

Relatively little is known about the distributions of the detailed recordings of weight at 

birth on birth certificates. It is not beyond the 

realm of possibility that higher frequencies of 

live births may be recorded at certain rounded 

weights (whole pounds, half pounds, or quarter 

pounds) than at the intervening ounces. If such 

clusters exist, the class 2,001-2,500 grams 

would represent an overcount of live births 

because it includes both 4?! and 5?4 pounds. 

The ideal solution would be for hospitals to 

have scales from which the metric weight can be 

read directly, and for the weight of the infant to 

be recorded on the birth certificate in exact 

grams. Such data could then be grouped into 

any desired weight classes at the time of 

tabulation. However, this goal is not likely to be 

achieved in the near future. In the interim, a 

statistical study of recorded birth weights would 

enable one to gauge the effect of such clusters 

and to determine whether or not the basic data 

are amenable to classification into finer birth 

weight categories. 

13 
WEIGHT AT BIRTH AND PERIOD 

OF GESTATION 

The effect of birth weight and period of 

gestation on neonatal mortality is available from 

two nationwide studies.s ~20 The low birth 

weight or preterm infant is subject to much 

higher risk of neonatal (or infant) death than 

other infants. In the nationwide study of 

neonatal mortality from linked birth and death 

records for the January-March 1950 cohort, 

neonatal mortality was found to be lower among 

“other” infants of low birth weight (164.7 per 

1,000 live births) than among the comparable 

group of white infants (175.8 per 1,000).20 This 

observation is in contrast with the usual relationship in mortality between infants of the two 

color groups. It was hypothesized that the 

reason for this atypical observation rests in the 

fact that, on the average, other infants weigh less 

than white infants with equal gestations. As a 

result, the low birth weight infants were felt to 

be more heavily weighted with infants having 

longer periods of gestation. for “other” than for 

white infants. If this hypothesis were true, more 

favorable gestations could possibly account for 

the better survival which was noted among low 

birth weight infants of other than white infants. 

Thc question which presents itself is: Among 

infants of equal weight, do other infants have 

longer gestations than white infants, on the 

average? 

To examine this hypothesis, the live births for 

1967 were tabulated by period of gestation, 

weight at birth, and color. In view of the 

inaccuracies in reported weeks of gestation, the 

data are shown separately for areas reporting 

LMP and areas reporting weeks of gestation 

(tables 5 and F). Because of the quality of the 

gestation data, the first attempt to examine 

gestation and birth weight together is for 1967, 

which is presumed to be the best of the available 

data. 

Areas Reporting LMP 

Among low birth weight infants in areas 

reporting LMP, 50.9 percent of the white infants 

and 58.3 percent of other infants were determined to be preterm ‘in 1967 (table F). The 

gestational age for infants in these areas was 

computed from the LMP date to the date of 

birth. In contrast to the hypothesis that lower 

neonatal mortality among other than white irifants of low birth weight is associated with 

greater maturity, the data for 1967 suggest that 

there are higher proportions of preterm infants 

Table F. Percentage distribution	 of live births by period of gestation within major birth weight groups for areas reporting LMP and 

areas reporting gestation period, by color: United States, 1967 

Period of gestation 

Total . . . . . . . . . . . . . . . . . . 

Under 37weeks . . . . . . . . . . . . . . 

37 weeks and over . . . . . . . . . . . . . 

Under 28weeks . . . . . . . . . . . . . . . . 

28-31 weeks . . . . . . . . . . . . . . . . . . 

32-35 waaks . . . . . . . . . . . . . . . . . . 

36weeks, . . . . . . . . . . . . . . . . . . . 

37-39 weeks . . . . . . . . . . . . . . . . . . 

40weaks . . . . . . . . . . . . . . . . . . . . 

4142 weeks . . . . . . . . . . . . . . . . . . 

43weeks And over . . . . . . . . . . . . . . . 

Areas reporting LMP’ Areas reporting gestation period 

2,500 grams 2,501 grams 2,500 grams 2,501 grams 

or less or more or less or more 

All All All 

White other White other White other 5= 

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 

50.9 58.3 5.4 10.8 48.6 49.6 2.1 3.6 

49.1 41.7 84.6 89,2 51.4 50,4 97.9 96.4 

t 

6.3 10.2 0.1 0.4 6.1 7.5 0.0 0.0 

9,3 11.9 0.3 0.7 8.1 10.0 0.0 0.1 

25.9 26.6 2.5 5.5 20.2 18.0 0.4 0.7 

9.4 9.6 2.5 4,2 14.1 14.1 1.6 2.8 

33.3 26.9 36.1 43.7 22.0 16.2 13.4 11.7 

7.4 6.4 24.8 20.7 27.8 33.4 76.7 81.5 

5.9 5.3 24.7 18.0 1.4 0.7 7.0 2,8 

2.4 3.2 7.0 6.7 0,2 0.1 0,9 0.5 

1 Refers only to births o~~urring within thase registration areas—8altimcsre, Californiar District of Columbia, Minnesota and 

New York City. 

14 
among the “other” group than among a comparable group of low birth weight white infants. 

The excess is evident in each of the four subdivisions included in the group, under 37 weeks. 

From 37 through 42 weeks, there are higher proportions of white than of other infants, and it is 

only in the longest gestation periods (43 weeks 

and over) that the proportion of other infants 

once again exceeds that of white infants. 

For the remaining birth weight groups in the 

areas reporting LMP, there were proportionately 

more infants other than white in each of the 

gestation groups under 40 weeks than white 

infants. In each of the two major weight groups, 

it would seem that there were more preterm 

infants among other infants than among white 

infants in 1967. This would contradict the 

earlier hypothesis associating lower mortality in 

this group of low birth weight infants with 

longer average gestations. However, these data 

based on LMP relate to the year 1967, which is 

17 years later than the January-March 1950 

study, and the areas reporting LMP are not 

representative of the country as a whole. 

The opposing tentative conclusions drawn 

from the study based on January-March 1950 

data and on data for the year 1967 may stem 

from either or both of two artifacts. The 

conclusions for the earlier data are based on 

gestational age classes using weeks of gestation 

as recorded on the birth certificates. The conclusions for 1967 are based on data for selected 

areas using gestations derived from date of LMP 

and date of birth. Thus, as one possibility y, the 

different results may be attributable to different 

measures of gestation. Second, the geographic 

coverage of the two sets of data are quite 

different: data for January-March 1950 covered 

the entire United States, while data for 1967 

included only the States of California and 

Minnesota, and the cities of Baltimore, District 

of Columbia, and New York City. In addition to 

the possible effects of these two artifacts, it is 

also possible that a real change may have 

occurred in the distributions of gestational ages 

of “other” infants of low birth weight over the 

18-year period. 

To explore this matter a step further, table G 

was prepared to present available data for the 

entire United States for the years 1951, 1960, 

and 1967. These years were selected to cover the 

time span of this report, but 1951 was used in 

place of 1950 because the necessary data for the 

latter were not available. The table presents the 

proportions of live born infants within each 

birth weight group who are defined as preterm– 

i.e., less than 37 completed weeks of gestation. 

On the whole, the proportion of preterm 

Table G. Percent of live births which are preterm, within specified birth weight groups by color: United States, 1951, 1960 and 1967 

w’-

8irth weight 

Total . . . . . . . . . . . . . . . . . . . 

2,500 grams or less . . . . . . . . . . . . . . 

2,501 grams ormora . ,. ., . , . . . . . . 

l,OOOgramsorless . . . . . . . . . . . . . . . 

1,001 -l,500grams . . . . . . . . . . . . . . . 

1,501 -2,000 grams , . . . . . . . . . . . . . . 

2,001 -2,500 grams . . , . , . . . , . . . . . . 

2,501 -3,000 grams . . . . . . . . . . . . . . . 

3,001 -3,500 grams . . . . . . . . . . . . . . . 

3,501 -4,000 grams . . . . . . . . . . . . . . . 

4,001 -4,500 grams . . . . . . . . . . . . . . . 

4,501 .5rOOOgrams . . . . . . . . . . . . . . . 

5,001 grams ormore . . . . . . . . . . . . . . 

1951 ‘ 1960 1967 

All All All 

White other White other White othar 

8.9 14.1 6,3 11.4 5.8 10,9 

47.6 45.6 50.7 49.6 48.9 50.9 

6.0 10.4 3.1 5.8 2.6 4.7 

97.1 93.8 98.0 97.2 97.8 97.3 

91.6 87.1 93.1 90.1 93.1 92.7 

72.1 69.3 75.2 73.8 74.2 75.5 

31.9 29.1 34.0 31.4 32.6 31.8 

8.5 10.1 7.2 8.0 6.5 7.5 

5.3 9.1 2.5 4.9 2.0 3.6 

5.3 11.0 1.8 4.7 1.3 3.0 

5.6 14.0 1.7 5.7 1.2 3.4 

7.5 16.1 2.0 8.1 1.1 5.0 

9.5 14.2 2.5 9.3 1.3 7.4 

1Excludes alI live births recorded in Connecticut and Massachusetts. 

15 
infants was higher for other infants than for in 1967 can be considered to be the best 

white in each of the years shown: available data at the present stage of developAll ment, it would seem that a new hypothesis —. 

White other presents itself for further testing–i.e., that 

1951 . . . . . . . . . . . . . . . . . . . . . 8.9 14.1 

1960 . . . . . . . . . . . . . . . . . . . . . 6.3 11.4 

1967 . . . . . . . . . . . . . . . . . . . . . 5.8 10.9 

Among low birth weight infants, some of the 

consistency disappears. In 1951 and 1960 for 

the low birth weight infants, there were proportionately fewer preterm infants among the other 

infants than among white infants. 

All 

White Other .— 

1951 . . . . . . . . . . . . . . . . . . . . . 47.6 45.6 

1960 . . . . . . . . . . . . . . . . . . . . . 50.7 49.6 

1967 . . . . . . . . . . . . . . . . . . . . . 48.9 50.9 

The observations for 1951 and 1960 agree with 

the data for January-March 1950, but the 

observation for 1967 does not. For all 3 years, 

however, the differences are small. These data 

are also affected to varying degrees by the 

problems associated with recorded weeks of 

gestation which were described earlier. Although 

the data include events which occurred throughout the United States and therefore avoid the 

artifact of geographic selection, the number of 

areas reporting LMP increased over this period 

of time. The areas reporting LMP accounted 

for no births in 1951, 14.3 percent of the total 

in 1960, and 17.1 percent in 1967. This increase 

would be expected to have some influence on 

the distribution of live births by gestational age. 

While one would tend to place more confidence 

in the data for 1967 than for 1951, over 80 

percent of the data for 1967 are still based on 

recorded weeks of gestation and as a consequence are felt to be quite unsatisfactory. The 

decline in the proportion of live births in the 

group at 36 weeks, with most of it apparently 

shifting to 37-39 weeks, as shown earlier in this 

report, has also clouded the issue, particularly in 

view, of the comparatively small differences in 

the percentages between the earlier and later 

time period. As a result, it is impossible to draw 

definite conclusions concerning the increase or 

lack of increase in preterm deliveries among 

white and other infants of low birth weight. 

However, if the data from areas reporting LMP 

higher proportions of infants weighing 2,500 

grams or less at birth are preterm among other 

infants than among white infants. 

Areas Reporting Weeks of Gestation 

The data for the areas reporting weeks of 

gestation are shown in table 5 for information 

purposes only, since they are considerably distorted by errors in the reported weeks of 

gestation. The concentration of so many live 

births in the “40-week” group has siphoned off 

enough events from other gestation groups to 

make it impossible to draw firm conclusions 

from the data. The heaping at 40 weeks appears 

more severe for other infants than for white 

infants, giving an illusion of lower proportions at 37-39 weeks, for example. However, 

one cannot discount the possibility that such 

observations may be due to errors in the 

reported weeks of gestation. Because the 

records from areas reporting weeks of gestation constitute over three-fourths of all live 

birth records, conclusions for the country as a 

whole cannot be inferred from the data. 

In summary, the LMP data for 1967 do not 

suggest that there is a lower proportion of 

preterm infants among other infants than among 

white infants. Rather, the suggestion is that for 

low birth weight infants as well as for infants 

weighing more than 2,500 grams at birth, the 

proportion of preterm infants is higher for other 

infants than for white infants. However, for low 

birth weight infants, the difference is not very 

great. Unfortunately, a similar comparison cannot be made of the data for 1950 or 1951 

because published data based on the LMP item 

are not available until after that time. 

The marked increase in the proportion of 

low birth weight infants among “other” 

infants between 1950 and 1967 does not 

seem to be associated with an increase in 

preterm delivery, although the gestation data 

are not entirely satisfactory. The data arc 

confounded by changes in reporting practices 

which limit their usefulness in quantifying 

16 
the changes in gestation distributions which 

occurred over the entire period 1950-67. 

AGE OF MOTHER 

Among the other factors which are known to 

be relate~ to the proportion of low birth weight 

infants is the age”of-the mother at the time-of 

the infant’s birth. As is shown in figure 4, the 

proportion of infants weighing 2,500 grams or 

less at birth is highest at the lower ages, drops to 

its lowest level for mothers 25-29 years of age, 

increases thereafter, and drops once again in the 

oldest group shown (45 years and over). Because 

of the marked differences in rates, the distribution of live births by age of mother could 

have a decided effect on the proportion of low 

birth weight infants born in any given year. Over 

the interval covered by this report, the distributions of live births by age of mother have 

undergone some rather important changes 

(tables 6 and 7). For example, the proportion of 

live births born to mothers under 25 years of age 

was markedly higher in 1967 than in 1950 (table 

H). This increase is particularly important because of the higher incidence of low birth weight 

among infants of mothers under 20 years of age. 

Also, for other than white infants, the 

markedly higher proportion of live births 

among rnoth&s under -25 years of age makes 

it important to consider age of mother as a 

possible associated factor which may be 

~elated to the increasing trend of low -birth 

weight among their infants which was shown 

in figure 3. 

The change in the incidence of low birth 

weight infants by age of mother is shown in 

table T and fimre 4. Data for the entire Year 

1950 & 1951 &e not available for this combination of variables. Instead, data from a special 

study for the period January-March 1950 were 

used.G0 The changes between the period 

January-March 1950 and 1967 are quite different for infants of the two color groups. 

For white infants, there was almost no change 

in the proportion of low birth weight infants 

between the two groups: the rates were 7.0 and 

7.1 percent (table J). Although there was a 

decrease in the proportion of low birth weight 

infants born to mothers under 15 years of age, 

the number of live births to this age group is but 

a very small part of the totaL The changes in the 

next higher age groups, where the bulk of the 

births occur, are either small or negligible. The 

largest increases in low birth weight infants 

among the white group occurred in the two 

oldest age groups. 

Among other than white infants, the proportion with low birth weight increased 

from 9.7 to 13.6 percent during the two 

time periods. There were no decreases; the 

incidence of infants of low birth weight increased for mothers in all age groups-the 

greatest increase occurring for mothers under 

Table H. Percentage distribution of live births by color and age of mother: United States, 1950 and 1967 

* 

I 1950 I 1967 

Age of mothar 

Total White 

All 

othar Total 

7 

White 

All 

other 

Total . . . . . . . . . . . . . . . . . . . I 100.0 100.0 100.0 100.0 100.0 100.0 

Under 15years . . . . . . . . . . . . . . . . . 0.1 0.1 0.7 0.2 0.1 1.0 

15-19 years . . . . . . . . . . . . . . . . . . . 11.8 10.4 20.6 16.9 14.9 26.9 

20-24 years . . . . . . . . . . . . . . . . . . . 31.9 31.8 32.6 37.2 38.2 32.4 

25-29 years . . . . . . . . . . . . . . . . . . . 28.8 29.7 23.2 24.6 25.7 19.6 

30-34 years . . . . . . . . . . . . . . . . . . . 16.8 17.4 13.2 12.5 12,7 11.6 

35-39 years . . . . . . . . . . . . . . . . . . . 8.3 8.4 7,5 6.5 6.5 6.3 

40-44 years . . . . . . . . . . . . . . . . . . . 2.1 2.1 2.0 1.9 1.9 2.0 

45and over . . . . . . . . . . . . . . . . . . . 0.1 0.1 0.2 0.1 0.1 0.1 

17 
------ ------

20 20 

WHITE 

\,\, ALL OTHER 

[ 

—	 Jm..Ma,. 1950 

-.-, -,-,- ,g~, 

15 15 

%, 

\+ 

\+ 

10 10 

,+, - ,----- %*,

~\- *\ .# %+ 

~ o~ ol~ under 15 15.19 20.24 25.29 30.34 35.39 40.44 45 a“d OVW Under 15 15.19 20.24 25.29 30.34 3539 40.44 45 and ciwr 

= 

~. 

. I 5 

: 20 20 

i! “4., 

JAN..MAR, 1950 “’..., 1967 

4. 

white ‘%, Wjlite 

,411 ~~h~~ ‘...,, ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, A,, ~t&~ .. . 15 ‘~ 15 -%, 4, 4, 

!1,1’’4,,,,,,,,,,,,,,, 

%..%,* ,,,,.,l, 

\ ‘%+ b “’’’’’’’’%,,,,,,,,,,,,,,,,l$}slll’ \ ?,,,

‘%,,,,, 10 

‘\ \, “’’%,,,,,,, 

10 \ 

\

\ ‘%,,,,, #,,,,,,,,,,,,,,,,,,,,,,,,,!l!ilLlll,,,.lllllrl!!!J,, -\ *#***”*.** * 

** “’’%,,,,,,,, ‘+* / 

**--	 + .-.-. ----”-----% %-. _--*.* 

% 

5 5 

0 I I I I I I I 1 0 ! I I I ! I I I 

der15 15.19 20.24 25.29 30.34 35.39 40.44 45 and over der15 15.19 20.24 25.29 30.34 35.39 40.44 45andovw 

AGE OF MOTHER [YEAR3) 

Figure4. Percent oflive&rths with low birth weiqhtby aqe Of mOther: lJnited States, January-March 1950and 1967. 

Table J. Percent of Iiva births with low birth weight by aga of mother and color: United States, January-March 1950 and the 

year 1967 

Total White other 

Age of mothar 

Jan-Mar Jan-Mar Jan-Mar 

967 Difference 1967 Difference 1967 )ifferenca 19501 1 19501 19501 

Total . . . . . . . . . . . 7.4 8.2 +0.8 7.0 7.1 +0.1 9.7 13.6 +3,9 - -

Under 15years . . . . , , . . , 15.1 17.2 +2.1 15.9 12.5 -3.4 14.7 19,5 +4,8 

15-19 years . . . . . . . . . . . 9.0 10.5 +1.5 8.0 8.5 +0.5 12.0 15.7 +3,7 

20-24 years . ., . . . . . . . . 7.3 7.7 +0.4 6.9 6.7 -0.2 9.6 13.2 +3,6 

25-29 years . . . . . . . . . . . 6.7 7.2 +0.5 6.5 6.5 8,4 11.8 +3,4 

30-34 years ., ...,.,... 7,2 7,9 +0.7 7.0 7.0 8,8 12.6 +3,8 

35-39 years . . . . . . . . . . . 7.7 9.1 +1.4 7.5 8.3 +0.8 9.0 13.3 +4.3 

40-44 years . . . . . . . . . . . 7.7 9.6 +1.9 7.5 9.1 +1.6 8,9 12.2 +3,3 

45yearsand over . . , . . . . . 6.1 8.6 +2.5 5.7 8.1 +2.4 7.4 10,8 +3.4 

‘Excludes all live births recorded in Massachusetts. 

18 
15 years of age (+4.8 percent). The second 

highest increase was for ages 35-39 years 

(+4.3 percent), and the increases for all of 

the other age groups ranged between +3.3 

and +3.8 percent. 

The two upper charts of figure 4 illustrate the 

changes in the proportion of low birth weight by 

age of mother between January-March 1950 and 

the year 1967. They depict, graphically, the 

relatively small change for white infants and the 

relatively constant substantial increase for other 

infants. The smallest arithmetic increase in the 

latter group exceeds the largest increase in the 

white group. 

The two lower charts compare the same data 

for the two color groups, first for the JanuaryMarch cohort and then for the year 1967. The 

differential between the two color groups increased over the period covered in this report. 

For 1967, the difference between the color 

groups is greatest among mothers under 20 years 

of age, and least among the oldest group. 

Both the distribution by age of mother and 

the age-specific rates of low birth weight affect 

the proportion of low birth weight infants for 

any group. For planning purposes, it is important to decide which of the two factors has the 

greatest effect on the levels for infants in the 

two color groups. A further examination of the 

data reveals that the difference in the distributions of age of mother has little effect on the 

color-specific rates; almost all of the difference 

is associated with differences in the age-specific 

rates of low birth weight. Thus, one may 

conclude that the stability of the proportion 

of infants of low birth weight among white 

infants and the increasing trend among other 

infants between January-March 1950 and the 

year 1967 is not attributable to the changing distributions of live births by age of 

mother. 

BIRTH ORDER . 

Another factor associated with the proportion 

of low birth weight infants is order of birth. The 

study for January-March 1950 showed that for 

all births the rates are lowest for second births 

and are elevated for first births and higher birth 

orders:6 O 

Total-birth order 

All birth orders . . . . . . . . . . 

First . . . . . . . . . . . . . . . . . 

Second


Third . :::::::::::::::


Fourth . . . . . . . . . . . . . . . .


Fifth and over . . . . . . . . . . . .


EEE 

Percent 2,500 grams 

or less 

7,4 7.0 9.7 

II

7.7 7.2 11.8 

6.9 6.5 10.1 

7.2 6.9 8.9 

7.5 7.4 8.3 l-_l-

7.7 7.4 8.5

Distributions by birth weight and total-birth 

order are not routinely published for the United 

States and therefore the trends in proportions of 

low birth weight infants for other years could 

not be examined directly by birth order. However, the range in the proportions is smaller by 

order of birth than was the range by age of 

mother. Therefore, the effect of a changing 

distribution of total-birth orders is probably less 

than the effect of mother’s age, and it would 

probably have less influence on the proportion 

of low birth weight infants for white and other 

infants. This inference is based on the relative 

magnitude of the proportions of low birth 

weight infants by age of mother and by birth 

weight, and cannot be demonstrated conclusively because of the lack of the basic data. 

PLURALITY 

Infants of plural births weigh, on the average, 

considerably less than those of single births. 

Thus plurality is also a factor which could affect 

the proportion of low birth weight infants in 

any given population. If the proportions of 

plural births were increasing for other infants 

but not for the white infants, a relative increase 

in the proportion of low birth weight infants 

could occur. Table K shows the rate of plural 

births per 1,000 live births. Although the rate is 

higher among other than white infants, it is not 

increasing. It must be concluded, therefore, that 

the increasing trend in low birth weight among 

other than white infants is not the result of 

increases in the rate of plural births. 

19 
TableK, Proportionof Pluralbirthsby color: UnitedStates, that there has not been a gradually decreasing 

1950-67 sex ratio. Moreover, the changes in sex ratio s from year toyear are relatively minor compared Year EEE12rLto the increasing trend of low birth weight 

1950 . . . . . . . . . . . . . . . . . . . . . . . . . 

1951 . . . . . . . . . . . . . . . . . . . . . . . . . 

1952 . . . . . . . . . . . . . . . . . . . . . . . . . 

1953 . . . . . . . . . . . . . . . . . . . . . . . . . 

1954 . . . . . . . . . . . . . . . . . . . . . . . . . 

1955 . . . . . . . . . . . . . . . . . . . . . . . . . 

1956 . . . . . . . . . . . . . . . . . . . . . . . . . 

1957 . . . . . . . . . . . . . . . . . . . . . . . . . 

1958 . . . . . . . . . . . . . . . . . . . . . . . . . 

1959 . . . . . . . . . . . . . . . . . . . . . . . . . 

1960 . . . . . . . . . . . . . . . . . . . . . . . . . 

1961 . . . . . . . . . . . . . . . . . . . . . . . . . 

19621 . . . . . . . . . . . . . . . . . . . . . . . . 

18831 . . . . . . . . . . . . . . . . . . . . . . . . 

1964 . . . . . . . . . . . . . . . . . . . . . . . . . 

1965 . . . . . . . . . . . . . . . . . . . . . . . . . 

1966 . . . . . . . . . . . . . . . . . . . . . . . . . 

1967 . . . . . . . . . . . . . . . . . . . . . . . . . 

Rate per 1,000 live births 

20.9 20.2 25.3 

20.7 20,0 25.4 

20.7 19.9 25.6 

21.0 20.1 26.9 

20.9 19.9 26.4 

21.1 20.2 26.5 

21.3 20.4 26.6 

20.5 19.4 26.7 

20.6 19.5 27.0 

20.6 19.5 27.0 

20.4 19.3 26.3 

20.2 19.0 26.6 

19.5 18.5 24.8 

19.8 18.6 26.1 

19.9 18.7 26.1 

20.1 19.0 25.8 

19.8 18.8 24.6 

19.7 18,8 24.1 

among other than white infants. As with age of 

mother and plurality, a changing trend in the sex 

ratio at birth cannot account for the observed 

trends in the proportion of low birth weight 

infants. 

PLACEOFBIRTH ANDATTENDANT 

The comparability of the data on length of 

gestation over the years 1950-67 has been 

Table L. Sex ratio of live births by color: United States, 

‘ Figures by color excluded for New Jersey. 

SEX 

Similarly, it can be shown that the increasing 

trend in low birth weight among other than 

white infants is not related to achange in the sex 

ratio at birth. It is known that male infants are, 

on the average, heavierthanfemde infants. Thus 

if the sex ratio (males per 1,000 females) were 

decreasing, there would be fewer heavier babies 

among the live births, and the proportion oflow 

birth weight infants would be expected to 

increase. However, from table L, i;is apparent 

1950-67 

f 

Year 

1950 . . . . . . . . . . . . . . . . . . . . . . . . . 

1951 . . . . . . . . . . . . . . . . . . . . . . . . . 

1952 . . . . . . . . . . . . . . . . . . . . . . . . . 

1953 . . . . . . . . . . . . . . . . . . . . . . . . . 

1954 . . . . . . . . . . . . . . . . . . . . . . . . . 

1955 . . . . . . . . . . . . . . . . . . . . . . . . . 

1956 . . . . . . . . . . . . . . . . . . . . . . . . . 

1957 . . . . . . . . . . . . . . . . . . . . . . . ,. 

1958 . . . . . . . . . . . . . . . . . . . . . . . . . 

1959 . . . . . . . . . . . . . . . . . . . . . . . . . 

1960 . . . . . . . . . . . . . . . . . . . . . . . . . 

1861 . . . . . . . . . . . . . . . . . . . . . . . . . 

1962’ . . . . . . . . . . . . . . . . . . . . . . . . 

1963’ . . . . . . . . . . . . . . . . . . . . . . . . 

1964 . . . . . . . . . . . . . . . . . . . . . . . . . 

1965 . . . . . . . . . . . . . . . . . . . . . . . . . 

1966 . . . . . . . . . . . . . . . . . . . . . . . . . 

1967 . . . . . . . . . . . . . . . . . . . . . . . . . 

Males perl,OOOfemales 

1,054 ,058 1,025 

1,052 ,058 1,018 

1,051 ,059 1,011 

1,053 ,058 1,025 

1,051 ,056 1,020 

1,051 ,056 1,020 

1,052 ,056 1,028 

1,050 ,055 1,025 

1,050 ,054 1,022 

1,049 ,054 1,023 

1,049 ,055 1,018 

1,050 ,055 1,023 

1,048 ,052 1,024 

1,053 ,057 1,030 

1,047 ,052 1,022 

1,051 ,056 1,028 

1,049 ,053 1,025 

1,050 ,056 1,020 

‘ Figures by color excluded for New Jersey. 

. 

20 
challenged in this report on the basis of improper recording of weeks of gestation on a large 

proportion of live birth certificates. With birth 

weight, as well, one might question the comparability of the data over the 18-year period. 

Between 1950 and 1967, the proportions of live 

births which occurred in hospitals increased, and 

the increase was much greater for other infants 

than for white infants (table M). For infants 

who were born in hospitals, where scales are 

available and easily accessible, the recording of 

birth weight is presumably more accurate than 

for infants born at home. Thus one might well 

consider whether the shift in the distribution by 

birth weight among “other” infants is real or 

whether it reflects the greater use of hospitals in 

1967 than in 1950. 

Over the period of time covered by this study, 

I increasing proportions of live births have ocTable M. Percent of live births which occurred in hospitals and 

percent with low birth weight by color: United States, 1950-67 

Year 

1950 ..,...., 

1951 . . . . . . . . 

1952 . . . . . . . . 

1953, . . . . . . . 

1954 !.,,.,,. 

1955 ...,.... 

1956 ..,...., 

1957 .,,..... 

1958 . . . . . . . . 

1959 ...,.... 

1960 ..,..... 

1961 ,,.,,, ., 

19624 . . . . . . . 

.	 19634, . . . . . . 

1964 .,.,,,.. 

1965, .,..... . 1966 . . . . . . . . 

1967 . . . . . . . . 

White , 

01 

Born Low Born Low 

in birth in birth 

hospital weight hospital weight 

92.8 17.1 57.9 110.2 

94.4 17.0 62.4 110.7 

95.7 17.0 66.4 111.1 

96.5 17.0 70.3 111.3 

97.0 16.8 73,1 111.3 

97.5 16.8 76.0 ‘11.7 

98.0 26.7 78.7 212.0 

98.2 36.8 81.1 312.4 

98.4 36.8 82.5 312.9 

98.7 6.8 83.7 12.9 

98.8 6.8 85.0 12.8 

98.9 6.9 86.0 13.0 

99.0 7.0 86.9 13.1 

99.1 7.1 87.9 13.6 

99.1 7.1 89.0 13.9 

98.9 7.2 89.8 13.8 

99.3 7.2 91.6 13.9 

99.4 7.1 92.9 13.6 

* Excludes all Iive births recorded in Connecticut and Massachusetts. 

aExcludes all live births recorded in Massachusetts for entire 

year and Connecticut for part of year. 

sExcl udes all live births recorded in Massachusetts. 

# Figures by color excluded for New Jersey. 

curred in hospitals for both color groups: 

* 

All White Place of delivery and other 

attendant 

1950 1967 1950 1967 ‘ 

Percentage distribution 

Total . . . . . . . . 100.0 100.0 100.0 100.0 

Born in hospitals . . . . . 92.8 99.4 57.9 92.9 

Born outside hospitals: +- I 

Physician . . . . . . . . 5.9 I 0.3 14.3 1.1 

Midwife, other, not 

specified . . . . . . . 

The increase in hospital delivery was especially 

great among “other” infants (from 57.9 to 92.9 

percent), while the decreases in births outside 

hospitals was marked whether physicians or 

other attendants were present. The changes for 

white infants were in the same directions as for 

other infants (an increase for hospital deliveries, 

and decreases for the other two groups), but 

were much smaller in magnitude. Since the 

changes were smaller for white than for other 

infants, the effect on the birth weight distributions, if any, would also be expected to be 

smaller for white infants. This possibility gives 

rise to the question: Could such a statistical 

artifact be responsible for the shift in the 

distributions of “other” infants toward lower 

birth weights? 

Most of the increase in the hospital delivery 

occurred between 1950 and 1960. The arithmetic increase from 57.9 to 85.0 percent between these 2 years (27.1 percent) was over 

three times the increase between 1960 and 1967 

(7.9 percent). If the changing pattern of recorded birth weights is associated with the 

increase in hospital deliveries, one would expect 

a greater effect on birth weight among other 

than white infants during the period 1950-60 

than 1960-67, and this pattern is reflected in the 

data. The increase in low birth weight among 

these infants was about three times as great 

between 1950 and 1960 (2.6 percent) as between 1960 and 1967 (0.8 percent). This observation would be consistent with a hypothesis 

associating the increase in low birth weight with 

the increase in hospital deliveries. 

Another approach is to consider whether the 

magnitude of the difference in percentage of low 

birth weight for other than white infants 

21 
between 1950 and 1967 could be attrl%uted to 

misreporting of weight at birth in 1950, and 

thus be due to artifacts. For the sake of 

,discussion, one could hypothesize that, in real­

,ty, the birth weight distribution did not change 

between 1950 and 1967, but that the data may 

reflect better reporting of weight at birth in 

1967 because of the marked increase in the 

proportion of births which occurred in hospitals. 

Under this hypothesis, how would the distribution of live births have appeared in 1950, based 

on the 1967 experience? This line of questioning 

is pursued in table N. The first column contains 

the number of “other” live births in 1950 

according to recorded weight at birth. AL 

infants whose birth was recorded in Connecticut 

(1,428) and Massachusetts (2,243) have been 

excluded because the official records of these 

States did not request weight at birth. The 

second column contains the expected numb er of 

live births which would have been recorded in 

the various weight groups in 1950 under the 

hypothesis that live births in that year were 

zctually distributed in the same proportions as 

in 1967, and that the differences between the 

‘LVVO distributions are aue to erroneous recording 

of birth weight for’ infants delivered outside 

hospitak in 1950. The third column reflects the 

differences between the frequencies in each of 

the birth weight groups. 

One notable difference between the observed 

and expected number of births is the marked 

decrease from 27,766 to 1,694 in the number of 

‘infants with weight unspecified. This difference 

of 26,072 includes infants whose birth records 

failed to include a specified birth weight in 

1950, and about half of them were born in 

hospitals. In addition to the 26,072 infants with’ 

weight unspecified in 1950 which are represented in actual weight categories in the expected distribution, another 83,886 seem to 

have been” allocated to an improper weight 

category in the observed distribution. In all, for 

ihe 1950 group of other than white infants to 

have really had a distribution like that of 1967, 

there would have had to be a change in the 

weight group allocation of 109,958 of the 

486,851 births (23 percent). 

Looking at the cells in more detail, if the 

birth weight distributions of the live births in 

1950 were really the same as in 1967, only 

109,286 live births weighing 3,501 grams or 

Table N. Birth weight distribution of infants of Negro and other races observed in 1950, and as expected based on the 

1967 experience: United States 

Birth weight 

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1,060 grams or less . . . . . . . . . . . . . . . . . . . . . . . 

1,001-1,500 grams . . . . . . . . . . . . . . . . . . . . . . . . 

1,501-2,000 grams . . . . . . . . . . . . . . . . . . . . . . . . 

2,001 -2,500 grams . . . . . . . . . . . ..o. . . . . . . . . . 

2,501 -3,000 grams . . . . . . . . . . . .. o... . . . . . . . 

3,001 -3,500 grams . . . . . . . . . . . . . . . . . . . . . . . . 

3,501 -4,000 grams . . . . . . . . . . . . . . . . . . . . . . . . 

4,001 -4,500 grams . . . . . . . . . . . . . . . . . . . . . . . . 

4,501 grams or more . . . . . . . . . . . . . . . . . . . . . . 

Not stated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1Based on distribution of live-born infants in 1967. 

2Excludes data for Connecticut and Massachusetts. 

Observed Expected 1 Difference 

I I 

Number of live births 

2486,851 486,851 

2,632 5,258 +2,626 

4,073 

8,963 

6,060 

12#69 

+1 ,987 

+3,906 +18,846 

31,376 41,703 +10,327 

98,334 

162,478 

128,235 

181,746 

+29,901 

+19,268 +49,1 69 

104,540 86,433 -18,107 

31,613 18,554 -13,059 -41,943 

15,076 4,299 -10,777 

27,766 1,694 -26,072 -26,072 

22 
more would have been expected in the year 

1950, whereas 151,229 were actually so designated. This difference of 41,943 far exceeded 

the expected decrease in the number with birth 

weight unspecified (26,072). Furthermore, the 

two differences do not offset each other since 

both have decreased. 

At the other end of the birth weight sczile, 

under the present hypothesis, the expected 

number of low birth weight infants should have 

been 65,890 instead of the 47,044 which was 

observed, an understatement of 18,846 infants 

in these weight groups. Numerically, it is possible that all of the increase could have come from 

the category with weight not stated (26,072). 

However, one may question that such a large 

proportion (72 percent) of the group with 

weight unspecified should have been low birth 

weight infants, when only about 13 percent of 

all infants were in that weight class. 

In all of the weight groups of 3,501 grams or 

more, it would also be numerically possible that 

the decrease of 41,943 infants would have had 

their birth weight misreported in 1950 so as to 

fall almost completely within the categories 

between 2,501 and 3,500 grams. However, the 

arithmetic coincidences which are required to 

explain away all of the changes on the basis of 

statistical artifacts challenge the imagination. 

It seems much more reasonable to accept the “ 

fact that most of the 58 percent of other than 

white infants who were delivered in hospitals in 

1950 were probably actually weighed and satisfactorily recorded. An additional 14 percent of 

infants were born outside hospitals, but their deliveries were attended by physicians, and their 

weights were also probably fairly well reported. 

If one accepts these assumptions, then the remaining 28 percent of live births delivered outside hospitals which were attended by nonphysicians would then have to account for the entire 

distortion of the birth weight data. To maintain 

that the phenomenon is due entirely to misreporting of birth weight for nonhospital births 

delivered by nonphysicians in 1950 would imply 

that as many as half of the birth weights of this 

28 percent would have been overstated. 

The average weight of infants in the observed 

distribution is 3,245 grams, and in the expected 

distribution 3,079 grams, a difference of 166 

grams, on the average. If this effect on the 

distribution of all infm-ts were attributable to 

overstatement among half of the infants who 

were born outside hospitals and whose birth was 

attended by nonphysicians, the overstatement 

for the latter group would have averaged 1,230 

grams (about 2 lbs. 9 oz.) for each infant. The 

magnitude of this overstatement in relationship 

to the median weight of 3,120 grams (6 Ibs. 14 

oz. ), is quite large and may be magnified to 

some extent by the assumption that the birth 

weights recorded for the 14 percent delivered by 

physicians outside hospitals were adequately 

recorded. In any event, this degree of misreporting is felt to be too great to be an acceptable 

explanation of the total difference between the 

observed and expected distributions. The truth 

probably lies somewhere between the two extremes. If the difference between the observed 

and expected distributions of birth weights of 

other infants is too great to be attributed to 

misreporting alone, neither can the entire difference reasonably be attributed to an actual shift 

in the birth weight distribution. 

An alternate approach to estimate the possible effect of incorrect reporting of birth weight 

for nonhospital births is to assume that the 

entire difference in the birth weight distributions between infants born in hospitals and 

infants born outside hospitals in any given year 

is due to erroneous recording of birth weight 

information for infants born outside hospitals. 

This assumption implies that, in reality, the true 

proportionate birth weight distributions are 

identical for (a) infants born ;n hospitals, (b) 

infants delivered by physicians outside hospitals, 

and (c) infants delivered by nonphysicians outside hospitals. Any differences in the observed 

proportions are assumed to be artifacts due to 

incorrectly recorded birth weight. The colorspecific distributions are not identical to each 

other. 

Between 1950 and 1967, there were marked 

changes in the proportions of infants by place of 

delivery and attendant, as has already been 

demonstrated. If these proportions for 1967 are 

used to weight the birth-weight-specific proportions in each place of delivery and attendant 

group in 1950, the expected distributions for 

1950 reflect the combined effect of the hypothetical error in recorded birth weights in 1950 

and also the changing proportions in place of 

23 
delivery and attendant groups between 1950 and 

1967 (table O). 

Under these assumptions, the expected 

changes in the distribution of white infants 

closely resembled the actual observed distribution in 1967. However, for “other” infants, 

the changes in the birth weight distributions 

would have accounted for only half of the actual 

increase in low birth weight infants between 

1950 and 1967. The remainder, unexplained by 

the assumed error in recorded birth weights, or 

to the changing patterns of place of delivery and 

attendants, may possibly be attributable to a 

genuine increase in the proportion of low birth 

weight infants in this group. 

This line of reasoning requires an assumption 

about birth weight that is presently not subject 

to verification. There is no way of reweighing 

the infants to validate their birth weights. In 

addition, this method assumes that the proportion of infants in the three attendant groups is 

constant for each birth weight group within each 

of the color groups of infants. To the extent 

that these assumptions are valid, ‘the method 

yields a crude estimate of the possible effect of 

errors of recorded weight. Ideally, one would 

like to determine conclusively whether increases 

in the proportion of low birth weight among 

other than white infants are real or are due to 

other factors, such as more complete registration 

of live births, more complete reporting of weight 

at birth, or more accurate reporting of birth 

weight. In contrast to laboratory situations 

where an experiment can be repeated any 

number of times, it is impossible to replicate the 

same birth weight information under each of a 

number of alternative situations after the fact. 

For example, one cannot document the birth 

weight of infants who were not registered in 

1950 but whose counterparts were registered in 

1967. Also, one cannot determine, even within a 

given year, to what extent the recorded birth 

weight of the same infant would have differed if 

it had been born in a hospital instead of 

elsewhere. Instead, one must rely on distributions of events occurring at different points in 

time, coupling the obs&vations with- what is 

known about registration, and drawing inferences rather than deductions. 

Tabulations of live births by color, weight at 

birth, and place of delivery (hospital or nonhospital) are not published annually. Such data 

have been found only for 2 of the 18 years 

included in this report, 1950 and 1951. The 

Table O. Estimate of the effact of changing proportions of births by place of delivery and attandant on waight-specific distribution of 

live births by color: United States, 1950 and 1967 

Weight at birth 

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2,500 grams orless, , .,...,..,.. . . . . . . . . . 

2,501 grams ormore . . . . . . . . . . . . . . . . . . . . . 

1,000 grams or less . . . . . . . . . . . . . . . . . . . . . . . . 

1,001-1,500 grams . . . . . . . . . . . . . . . . . . . . . . . . 

1,501 -2,000 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

2,001 -2,500 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

2,501 -3,000 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

3,001 -3,500 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

3,501 -4,000 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

4,0014,500 grams . . . . . . . . . . . . . . . . . . . . . . . . . 

4,501 grams ormore . . . . . . . . . . . . . . . . . . . . . . . 

White 

1950 I 1967 

Observed Theoretical* observed 

100,000 

7,059 

92,941 

401 

554 

1,310 

4,794 

17,805 

38,324 

27,519 

7,595 

1,698 

100,000 100,000 

7,113 7,112 

92,667 92,889 

402 437 

552 552 

1,321 1,338 

4,838 4,785 

18,086 18,342 

38,730 36,716 

27,350 27,101 

7,299 7,321 

1,412 1,408 

All other 

1950 1967 

Observed Theoretical 1 Observed 

100,000 100,000 100.000 

10,246 11,936 13,582 

89,753 88,064 86,418 

573 729 1,084 

887 1,019 1,249 

1952 2,290 2,653 

6,834 7,898 8,596 

21,420 25,157 26,432 

35,392 37,825 37,461 

22,771 19,205 17,815 

6,886 4,495 3,824 

3,284 1J82 886 

‘ Derived by applying the 1967 proportions of live births delivered in hospitals, delivered by physicians outsida hospitals, and de1ivered by midwives and others outside hospitals to the weight-specific distributions of each of these categories in 1950. 8irths with 

birth weight unspecified ara excluded. 

24 
experience of these 2 early years may not be 

representative of the entire period, but the data 

are indicative of events at midcentury. For the 

specified years, the proportions of low birth 

weight infants in each of the groups are as 

follows: 

Place of delivery and 

attendant 

* 

Total ..,.,... 7.1 7.0 10.2 10.7 

Born in hospitals . . . . , 7.1 7.1 12.3 12.5 

Born outside hospitals: 

Physician . . . . . . . , 6.2 6.4 8.8 8.8 

Midwife, other, not 

speoified . . . , . . , 6.7 7.0 6.3 6.8 

1Besed only on stated birth weights. 

For white infants, the proportion of infants 

born in hospitals who were of low birth weight 

remained unchanged while there were increases 

among those born outside hospitals. In contrast, 

for “other” infants, there was an increase in the 

proportion of low birth weight infants among 

those delivered in hospitals. For those born 

outside hospitals, the proportion of infants who 

were of low birth weight remained unchanged 

for those delivered by physicians, but increased 

for those delivered by nonphysicians. Since the 

data are for successive years 1950 and 1951, 

they do not permit one to draw conclusions 

about trends in terms of the entire period 

covered by this study. 

Another factor which may have affected the 

distribution of birth weight of live born infants 

is the degree of completeness of live birth 

registration. Tests of completeness were carried 

out for the period January-March 1950 and 

again in 1970 for infants born during the 5-year 

period 1964-68.61 The percentage completeness 

of registration of live births of white infants was 

estimated as 98.6 for January-March 1950 and 

99.4 for 1964-68. Corresponding percentages for 

other live born infants are 93.6 and 98.0. Since 

1950, the proportion of low birth weight infants 

has remained almost stationary at 7 percent for 

white infants, and it has increased from 10.2 to 

13.6 percent for other infants (table 4). Perhaps 

part of the increase for the latter group maybe 

associated with more complete registration of 

live births, but this factor is probably of less 

importance than some of the other factors 

which have been mentioned. 

One characteristic of the change in the distribution of birth weight for other than white 

infants which is worthy of mention is the 

pervasiveness of the phenomenon. Each category 

of birth weight was affected to some degree, 

resulting in a shift of the entire distribution 

toward lower birth weight (table P). There were 

actually decreases in the numbers of live births 

in weight groups over 4,000 grams (8 lb. 14 oz.) 

between 1950 and 1967, at the same time that 

there were increases in the lower weight groups. 

For example, the number of live born infants in 

the weight group over 4,000 grams declined 

from 46,689 in 1950 to 28,093 in 1967 despite 

a 22 percent increase in the number of live 

births in the same period (table 3). Such changes 

may reflect, to some extent, determined efforts 

to control the weight of fetuses in order to avoid 

complications associated with the delivery of 

large fetuses. For example, one such condition, 

overweight in a fetus which is related to diabetes 

in the mother, is amenable to control in the 

prenatal period if the mother is under the care 

of a physician. The decreases in the frequencies 

in the upper weight groups may reflect, in part, 

increased prenatal care and the control of 

adverse maternal conditions. Such changes 

would constitute some of the re~ factors which 

Table P. Percant change in numbar of Iiva births by birth weight 

and color: United States, 1950 to 1967 

Birth weight 

Total . . . . . . . . . . . . . . . . . . . 

2,500 grams or less . . . . . . . . . . 

2,501 grams or more . . . . . . . . . 

1,000 grems orless . . . . . . . . . . . . . 

1,000-1,500 grams . . . . . . . . . . . . . 

1,501-2,000 grams . . . . . . . . . . . . . 

2,001-2,500 grams . . . . . . . . . . . . . 

2,501-3,000 grams . . . . . . . . . . . . . 

3,001-3,500 grams . . . . . . . . . . . . . 

3,501-4,000 grams . . . . . . . . . . . . . 

4,001-4,500 grams . . . . . . . . . . . . . 

4,501 grams ormore . . . . . . . . . . . . 

— 

Total White All 

other 

-0.9 -4.6 +22.0 

+8.5 -3.9 +61 .7 

-1.7 -4.7 +17.5 

+27 .5 +3.8 +130.7 

+10.6 -5.0 +71 .8 

+10.6 -2.6 ffi5.8 

+6.0 -4.8 +53.4 

+6.7 -1.7 +50.6 

+0.6 -3.6 +29.1 

-5.9 -6.1 4.5 

-11.1 -8.0 -32.2 

-31.8 -20.9 -67.1 

25 
could affect the birth weight distributions in Infant mortalitv. in some of the other medicontrast to the statistical artifacts which have ‘ 

been emphasized earlier in this report. 

Although the exact effect of the various 

possible factors explaining low birth weight 

cannot be quantified, there is no question about 

the regularity of the changes in birth weight for 

other than white infants. This is in contrast to 

the erratic picture encountered in the review of 

data by gestational age, where faulty data were a 

major contributing factor. Although it cannot be 

stated categorically that the entire shift is due to 

real factors, neither can the change be dismissed 

summarily as a statistical artifact. 

Even though the full explanation is not 

known, there is no question about the fact that 

for 1967, the proportion of low birth weight 

infants for other than white infants (13.6 

percent) is almost double the proportion for the 

white group (7. 1 percent) (table 4). Having 

identified these two sharply contrasting groups 

with regard to low birth weight, epidemiological 

studies of the two groups are the next logical 

step. Such studies could supplement the information already included on vital records with a 

host of other factors, some of a biological, some 

of an environmental, and some of a socioeconomic nature. In past decades, studies of this 

kind have contributed to the solution of problems associated with a number of communicable 

diseases. The potential of such studies in solving 

the problems of prematurity is relatively unexplored. 

INTERNATIONAL COMPARISON 

In the United States, the proportion of live 

born infants weighing 2,500 grams or less at 

birth increased for all births from 7.5 percent in 

1950 to 8.2 percent in 1967 (table 4). That the 

level of mortality in the first year of life (infant 

mortality) is related to the proportion of low 

birth weight infants is generally accepted. However, the magnitude of the effect is not always 

recognized: the risk of death during the first 4 

weeks of life (neonatal death) among low birth 

weight infants is 30 times the risk for heavier 

infants.E Because of the relationship of low 

birth weight to infant mortality, an attempt was 

made to gauge the possible effect of the change 

in proportions of this magnitude on infant 

mortality rates. 

tally and economically advanced countries is 

considerably lower th& in the United States. 

For example, for 1966 the rates were:s 

Sweden 12.6 

Netherlands 14.7 

Australia 18.2 

United States 23.7 

White 20.6 

AU other 38.8 

Even when the data for the United States are 

limited to white births, a considerable differential remains between the rate for this country 

(20.6) and those for Sweden (12.6) and the 

Netherlands (14.7). In these two European 

countries, the proportion of low birth weight 

infants is reported to be about 5 percent.~ J62 A 

Swedish investigator has suggested that the 

difference between the infant mortality rates of 

Sweden and the United States may be due to a 

considerable extent to differences in the birth 

weight distributions in the two countries. 62 

The Committee on Maternal Nutrition of the 

National Research Council, National Academy 

of Sciences, considered the relation of nutrition 

to fetal growth and development. Its report 

states, in part: 

Among healthy women who have well-balanced diets and eat 

“to appetite,” the range in weight gains is very wide, The 

target of 20 to 25 pounds has been found to be a reasonable 

average. The Working Group agreed that gains in this range 

are consistent with the most favorable outcome of pregnancy 

and that a weight-reduction program that distorts normal 

gain should not be imposed during pregnancy. 

Current obstetric practice in the United States tends to 

restrict weight gain during pregnaocy. In view of the evidence 

available, one may raise the question of whether this practice 

is in effect contributing to the large number of Iow.birtk 

weight infants and to the high perinatal- and infantmortality-rates.63 

From an infant mortality study based on 

linked birth and death records for the cohort of 

infants born alive in the United States in 1960, 

it was determined that the risk of neonatal and 

infant death in relation to weight at birth was as 

follows:s 

Risk of Risk of Weight et birth Iinfant deeth neonatal daath 

Per 1,000 live births 

All weights . . . . . . . . 25.1 18.4 

2,500 grams or lass . . , , . . 190,3 171,6 

2,501 grams or more . . . , . 11.2 5.5 

26 
Using these rates, one can construct a set of 

hypothetical cohort death rates for a series of 

birth cohorts having varying percentages of 

births weighing 2,500 grams or less at birth: 

I Per 1,000 live 

births 

5.0, ,, . . . . . . . . . . . . . . . . . 20.2 13.8 

6.0, . . . . . . . . . . . . . . . . . . . 21.9 15.5 

7.0, . . . . . . . . . . . . . . . . . . . 23.7 17.1 

8,0 . . . . . . . . . . . . . . . . . . . . 25.5 18.8 

9,0, . . . . . . . . . . . . . . . . . . . 27.3 20.4 

10.0, . ., . . . . . . . . . . . . . . . . 29.1 22.1 

ll.O . . . . . . . . . . . . . . . . . . . . 30.9 23.8 

12,0 . . . . . . . . . . . . . . . . . . ., 32.7 25.4 

13,0, ,,, ,,, . . . . . . . . . . . . . 34.5 27.1 

14.0 . . . . . . . . . . . . . . . . . . . . 36.3 28.8 

16.0 . . . . . . . . . . . . . . . . . . . . 38.1 30.4 

If one group of live births has 5percent ofits 

births weighing 2,500 grams or less and experiences the weight-specific risks of death 

shown, the overall risk ofinfantdeathwcndd be 

expected to be 20.2 per 1,000 live births. If 

another group has 7 percent of its births 

weighing 2,500 grams or less at birth, the 

expected rate would be 23.7. If 14 percent of 

live births are of low birth weight, the expected 

SUMMARY AND 

SUMMARY 

The purpose of the present report is to 

summarize the changes in “prematurityy“ in the 

United States between 1950 and 1967. Because 

of incomplete registration of fetal deaths and 

deficiencies in the information recorded on fetal 

death records, the study is limited to live births. 

The report considem the distributions of live 

births in the United States according to two 

indexes of prematurityy—i.e., birth weight and 

period of gestation. The effort was stimulated 

by reports which implicated low birth weight as 

an important factor associated with trends in 

rate would be 36.3. The differences in these 

three expected rates are due entirely to the 

different proportions of low birth weight infants 

because the risks of death which were used for 

the birth weight distributions are identical 

throughout. Obviously, even small increases in 

the proportion of low birth weight infants can 

produce significant increases in the overall risk 

of infant or neonatal death. 

If in Western European countries such as 

Sweden or the Netherlands only 5 percent of 

live born infants weigh 2,500 grams or less at 

birth and the proportion in the United States is 

8 percent, the arithmetic weighting could account for perhaps half of the total difference 

between the infant mortality rates for the 

United States and the other two countries. The 

remaining half is assumed to be attributable to 

other factors. Although the cohort mortality 

rates and the traditional infant mortality rates 

are not arithmetically identical, they are sufficiently close to permit this kind of comparison. 

The hypothetical data are presented to indicate 

the marked effect which can be produced on 

neonatal and infant mortality rates by what may 

at first glance appear to be small differences in 

the proportions of low birth weight infants. 

Because of the high mortality among low birth 

weight infants, even small increases in proportions of low birth weight infants assume significance. They may be useful to clinical and 

public health planners in better understanding 

the nation’s position with regard to low birth 

weight and infant mortality. 

CONCLUSION 

infant and neonatal mortality. An increase in the 

proportion of low birth weight infants is n’ot 

evident in the national data for the total group 

of live births or for the white infants, who 

constitute 83 percent of the totaL However, for 

“other” infants an increase in the proportion of 

low birth weight infants is noted. The proportions of low birth weight infants for individual 

hospitals or cities can be affected by the 

changing nature of urban populations which, in 

recent years, have witnessed sizable immigrations of Negroes and other minority groups 

and out-migrations of the white group. In some 

instances, population shifts have markedly 

27 
changed the composition of a city’s population 

or of a hospital’s patient load. This demographic 

drift may account for increases in the proportion of low birth weight infants in individual 

urban hospitals. 

From the national data, one reaches a tentative conclusion that there appears to be relatively little change in the distribution of live 

births by period of gestation between 1950 and 

1967. The conclusion is qualified as “tentative” 

because of the apparent inaccuracies in the 

majority of recorded gestational ages for which 

the data are recorded in weeks. Conclusive data 

will probably never be available with regard to 

gestational age over this period of time, and 

conclusions for the period must remain somewhat conjectural. 

Observations with regard to birth weight are 

quite different. As a variable, birth weight is a 

more reliable item than gestation. Thus, one can 

say with more confidence that changes have 

occurred. The proportion of low birth weight 

infants increased from 7.5 to 8.2 percent over 

the period 1950-67 (table 4), which at first 

glance does not appear to be a large increase for 

the population of births as a whole. However, 

while there appeared to be little [change for 

white infants, the proportion of infants of low 

birth weight among other infants increased from 

10.2 percent to 13.6 percent. The increase is not 

attributable to changing distributions of live 

births by age of mother, plurality, or sex, and it 

is probably not due in its entirety to higher 

proportions of other than white infants who 

were delivered in hospitals with a resulting 

improvement in accuracy of reported birth 

weights. 

The trend in proportions of low birth weight 

infants for white and for other infants diverged 

over the period of the study. While the rates for 

white live births remained relatively stable, the 

rates for other infants increased. The divergent 

trends could not be explained on the basis of the 

factors which were available for comparison. 

The reporting of gestational age is subject to 

considerable inaccuracies, but the available evidence did not suggest that the increasing proportions of low birth weight for other than white 

infants were associated with concurrent increases of similar magnitudes in preterm deliveries. 

The present study has demonstrated a health 

problem in a significant and identifiable portion 

of the Nation’s population: an apparent increasing proportion of low birth weight among 

other than white infants. About 90 percent of 

these births are Negroes, and the remaining 10 

percent is composed of American Indians, Oriental, and other groups. The findings for this 

diverse group reflect the experience of its Negro 

majority, but they may not reflect similar 

patterns for the smaller minority groups such as 

American Indians or Orientals. 

One may ask whether the difference in trends 

between the white and the other groups are due 

to changes in their respective socioeconomic 

conditions between 1950 and 1967. Unfortunately, the national data for the period 1950-67 

do not provide infant mortality or prematurity 

data classified according to a socioeconomic 

indicator, and the data could not be examined in 

relation to this factor. The separation into white 

and other infants, of itself, provides a type of 

socioeconomic stratification, but it cannot provide any information according to socioeconomic stratification within each group. Thus, 

one cannot explore the possible relationship 

between trends in prematurity and the socioeconomic changes which may have occurred 

during the period covered by the study. 

QUALITY OF DATA 

One of the important side benefits of the 

study has been the redemonstration of some of 

the limitations of the Nation’s vital statistics 

system. The deficiencies in fetal death registration have been reported elsewhere.q4 In that 

report, it was estimated that a significant 

amount of underregistration of fetal deaths 

exists: perhaps 20-25 percent of fetal deaths of 

20 weeks or more of gestation are not registered. 

Reporting of fetal deaths for all of the States is 

required for at least those of 20 completed 

weeks or more of gestation or an equivalent, but 

fetal deaths at these gestational ages represent 

only about 20 percent of all fetal deaths. The 

failure to record birth weight on many fetal 

death records when the fetus is preterm introduces a bias in the birth weight data. These 

deficiencies, among others in fetal death registration, have precluded the production of fetal 

deatti and perinatal data of genuine utility to 

28 
researchers, program administrators, and planners. 

For live births, fortunately, the registration is 

very nearly complete. However, the same deficiencies which are found in the reported period 

of gestation for fetal deaths are found for live 

births as well. When gestation was recorded in 

weeks of gestation on the live birth records, 73.5 

percent of the gestational ages were reported to 

be 40 weeks (table C). When the gestational age 

was computed from the first day of the last 

menstrual period, only 22.8 percent. were allocated to 40 weeks. It is difficult to reconcile the 

inadequacies of the gestational age data with the 

high proportion of live births that are born in 

hospitals in the United States (98 percent in 

1967). In the absence of factual information, 

one might assume that gestational age data 

derived under such a system should be highly 

reliable, but the heapings at 40 weeks and at 36 

weeks, with indications of other less prominent 

clusters at other multiples of four, tend to 

negate this assumption. 

The Standard Certificates of Live Birth and 

Fetal Death, after which most of the States 

pattern their certificate forms, have recently 

been revised. The Surgeon General of the Public 

Health Service recommended to the States that 

these standard forms be introduced for regular 

use beginning in 1968. Most of the States have 

introduced new certificate forms as recommended, and the new items on these forms will 

increase the information available for future 

study. Among the changes on the forms are the 

date on which the last normal menses began, 

which should improve the gestational age data, 

and the education of father and mother, which 

should provide a socioeconomic indicator. These 

changes will, of course, not overcome the 

inadequacies of past data, but new data should 

form a base for better information in the future. 

CONCLUSION 

The early impetus for this report stemmed 

from an international comparison of perinatal 

and infant mortality which suggested that a 

higher proportion of low birth weight infants 

were born in the United States than in countries 

such as the Netherlands or Sweden, which have 

significantly lower infant mortality rates. While 

the present report concerns itself with the trends 

in “prematurity,” its importance extends to 

infant mortality and morbidity as well. 

Premature delivery and/or low birth weight 

are prime determinants of risk of infant death or 

impaired health. Their importance, long recognized by perinatal investigators, are not to be 

underestimated. The number of low birth weight 

infants who are born alive in the United States is 

over a quarter of a million infants annually— 

288,000 in 1967 alone. Because of the number 

of affected individuals, prematurity is regarded 

as a public health as well as a clinical problem. 

The clinical concern is reflected in the establishment of intensive care units for premature 

infants in hospitals, and the public health 

concern is reflected in the classification of 

prematurity in some States with other rehabilitative conditions under the federally assisted, 

crippled children’s programs. The medical care 

requirements for a low birth weight infant are 

great, sometimes requiring weeks or months of 

hospital care before the infant has attained the 

desired weight and can be released to join his 

family at home. Furthermore, mortality among 

low birth weight infants is higher than among 

other infants at least up to 5 years of age. 

The need for teamwork is no less now, for 

this particular health problem, than it was 

decades ago when communicable diseases played 

an important role in infant mortality. The search 

for solutions to the problem of low birth weight 

extends back beyond the point of delivery of 

the infant, to the care of the mother during 

pregnancy, and indeed to her formative years as 

well. At the time of an infant’s birth, it is too 

late to change its weight and, therefore, the 

concept of prevention assumes significance. Furthermore, because of the wide range of associated morbid conditions, and the long range 

effects of many of them, prevention assumes 

increased importance: prevention of lethal assaults by infections or drugs on the fetus, 

prevention of preterm delivery, and prevention 

of low birth weight among the newborn. These 

objectives call on the combined resources of 

clinical and preventive medicine. 

Statistical findings can assist in problem identification and in localizing associated factors, 

and thereby can further the efforts of other 

29 
investigators, However, the identification of a 

problem should not be confused with its solution. The definitive answers are not to be found 

in vital statistics alone, but must be sought in 

special surveys, epidemiological investigations, 

and clinical research., The present findings,rep1Moriyama, L M.: Recent changes in infant mortality trend 

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Health 45:1022-28 (Aug.) 1955. 

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No. 1000-Series 21-No. 6, Public Health Service. Washington. 

U.S. Goyemment Printing Office, July 1965. (reprint) 

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of Certain Biologic and Socioeconomic Factors to Fetalj Infant, 

and Early Childhood Mortality, by H. C. Chase, Albany, N.Y. 

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mother’s age (1962) 

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gestation on perinatal and neonatal mortality by ethnic group, 

Am. Pub. Health 54:1841-55 (Nov.) 1964. 

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children from birth to four years, Bn”t. M. J. 1:748-54 (Apr. 4) 

1953. 24fifienfeld, ~ M., ~d Pzkhurst, E.: A study ‘f ‘e 

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30 
development of cerebral pafsy; prelirnina~ report, Am. j. Hyg. 

53:262-82 (May) 1951. 

2S~enfeld, ~ M., ~d pmamanic~ B.: Association Of 

maternal and fetal factors with the development of epifepsy: I. 

Abnormrdities in the premtal and paranatal periods, j. A. M. A. 

155:719-724 (June 19) 1954. 

‘26L1henfel@ ~ M., pasamanick B., and Rogcrs~ ‘. ‘: 

Relationship between pregnancy experience and the develop 

ment of certain neuro-ps ychiatric disorders in childh oo~ Am. ]. 

Pub. Health 45:637-43 (May, pt. 1) 1955. 

27Li1ienfe1d, ~ M., ~d pa~mic~ B.: The association ‘f 

maternal and fetaf factors with the development of cerebral 

palsy and epilepsy, Am. J. Obst. & Gyrrec. 70:93-101 (JdY) 

1955. 28 pmamanic~ B., ~d Ljlienfeld, & M.: The mstiation ‘f 

maternal and fetaf factors with the development of mend 

defiaency: L Abnormalities in the prenatal and paranatai 

periods, ]. A. M. A. 159:155-60 (Sept. 17) 1955. 29 ~fiienfeld A. M., ad pasamaniclq B.: The association ‘f 

matemrd and fetal factors with the development of mental 

deficiency: H. Relationship to maternal age, birth order, 

previous reproductive loss and degree of mental deficiency, Am. 

J Merst. Deficiency 60:557-69 (Jan.) 1956. 

30DriUlen, C. M.: The incidence of mental and physical 

handicaps in school-age children of very low birth weight, 

Pediatrics 27:452-464 (Mar.) 1961. 

31 Baumgartner, L.: The public health significance of low 

birtb weight in the U.S.A, BUU World Health organ. 26:175-82, 

1962. 

s+~ifford, s. H.: High-risk pregnancy: I. Prevention of 

prematurity, the sine qua non for reduction in mental retardation and other necrologic dkorders, New EngZand j. Med 

271:243-49 Udy 30) 1964. 

33 Berendes, H. W.: Obstetrical complications apd menkd 

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the Scientific Study of Mental Retardation% Copenha&m, August 

7-14, 1964. 

34 Acheson, E. D.: Hospitaf morbidky in early life in relation 

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~elivery, Brit. J. Prev. &Social MerL 19:16473 (Oct.) 1965. 

35Drage,j.s.,and others : The ApgaI score as an index of 

infant morbidity, a report from the Collaborative Study of 

Ccrebraf Pafsy, Developmental Medicine and Child Neurology 

8:141-48 (Apr.) 1966. 

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in late neurogenic sequelae: I. Infants having birth wei@ts under 

1,5~1 grams, A. M. A. J Dis. Child 112:359-68 (Oct.) 1966. 

: Perirntal and environmental factors in late 

necrologic sequelae: IL Infants having birth weights from 1,500 

to 2,500 grams, A. M. A. j. Dis. Child 112:369-74 (Oct.) 1966. 38 Van den Berg B. J. ~d Yer-ushafmy, J.: me ‘elatiOnship 

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to mortality, morbkiity, and congenital anomafies, ]. Pe&at. 

69:531-45 (Oct.) 1966. 

39VernoW ~: prematurity and deafness: The magnitude and 

nature of the problem among deaf children, ExceP. Child 

33:289-98 (.Jan.) 1967. 

4 ODrillie~ C. M.: The incidence of mental and physicaf 

handicaps in school age children of very low birth weight (H), 

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41 Goldstein, H., and others: Perinatal factors associated with 

strabismus in Negro children, Am. J. Pub. Health 57:217-28 

(Fe~) 1967. 

Goldberg, L D., Goldstein, H., Quade, D., and Rogot, E.: 

Association of pennatal factors with bfindness in chifdren, Pub. 

Health Rep. 82:519-31 (.June) 1967. 

43 Katz, CL M., and Taylor, P. M.: The incidence of low 

birthwcigbt in children with severe mental retardation A. M. A. 

J. Dir. Child 114:8087 (July) 1967. 44 Chine ~ f..: The current status of fetal death rei+stration 

in the United States, Am. J Pub. Health 56:1734-1744 (Oct. ) 

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45 World Health Orgasrization: Manual of the Intematiod 

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Death, Sixth Revision, Adopted 1948. Geneva. World Health 

Organizatiorb 1957. 

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Session of the Expert Committee on Health Statistic%” Tech. 

Rep. Ser. Wld. Hlth. Org., No. 25, Geneva, 1950. 

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and Child Health: “Public health aspects of low birth weight. 

Third report of the Expert Committee on Maternal and Child 

Health. Tech. Rep. Ser. No. 217, Wld. Hlth. Org., Genev% 1961. 

48 *enCan Medic~ Association, Committee on Matem~ 

and Child Care of the Council on Medical Service: A Guide for 

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49 : Reducing infant mortality: Suggested a~ 

preaches, J. A.M.A. 193:130-139 (July) 1965. 

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New$om Infants, revised cd., Evanston, Ill., 1964. 

—: Nomenclature for duration of gestation, birth 

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and H. C. Hughes, Pediatrics 39:935-42 (June) 1967. 

54 Lubchenco, ~ 0., Hansman, C., Dressier, M., and BOY~ 

B.: Intrauterine growth as estimated from livebom birth-weight 

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55 Yemshalmy, J., van den Ber& B. J., Erhardt, C. L and 

Jacobziner, H.: Birth wei~t and gestation as indices of 

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weight, Developmental Medicine and Child Neurology 7:578-80 

(OCLj 1965. 

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99:3445 (Sept. 1) 1967. 

31 
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9. Public Health Service. Rockville, Md., Sept. 1971. p. 86. 

—ooo —


32 
LIST OF DETAILED TABLES


Table 1,


2.


3.


4.


5. 

6.


7.


Page 

Number of live births by period of gestation and color: United States, 1950-67 . . , . . . . . . . . . . . . . . . . 34 

Percentage distribution of live births by period of gestation and color: United States, 1950-67 . . . . . . . . . . . 36 

Number of live births by birth weight and color: United States, 1950-67 . . . . . . . . . . . . . . . . . . . . . . . 

Percentage distribution of live births by birth weight and color: United States, 1950-67 . . . . . . . . . . . . . . . 

Number of live births and parentage distribution by color, birth weight, and period of gestation for areas reporting


LMP and for areas reporting period of gestation: United States, 1967 , . . . . . . . . . . . . . . . . . . . . . . . .


Number of live births by age of mother and color: United States, 1950-67 . . . . . . . . . . . . . . . . . . . . . . . 

Percentage distribution of live births by age of mother and color: United States, 1950-67 . . . . . . . . . . . . . . . 

38 

40 

42 

43 

45 

33 
---

---

---

---

---

---

---

---

---

---

---

---

Table 1. Number of live births by period of gestation and color: United States, 1950-67 

[Data for the years 1951-54 and 1956-66 are based on a 50-percent sample of births; data for 1967 are based on a 20- to 50-percent simple] 

Period of gestation (weeks) 

Year and 

color Jnder 40 and 43 and Not Total 20-27 26-31 32-35 36 37-39 40 41J12 20 over over stated 

Total

— 

1950 . . . . . . ‘3,554,149 fM6 16,339 30,034 64,612 248,169 277,606 ?,618,609 !,507,647 97.321 13,441 2294,579 

1951 . . . . . . 3,750,850 664 19,050 10,636 65,694 226,320 303,842 ?,867,018 !,735,864 115,718 15,436 3237,606 

1952 . . . . . . 3,846,986 732 19,668 31,366 68,526 189,274 953,632 ?,925,638 !,764,940 j 60 96 4257,748 

1953 . . . . . . 3,902,120 858 20,644 11,062 68,310 172,126 153,438 1,021,636 !,844 ,956 176 80 s234,044 

1954 . . . . . . 4,017,362 -.. . . . . . . ..- . . . ..- . . . . . . . . . . . . 

1955 . . . . . . 4,047,295 . . . . . . .-. -.. ..- . . . ..- -.. . . . . . . 

1956 . . . . . . 4,163,080 ,208 ?3,092 !2,762 76,924 158,234 155,616 J,153,534 -.. . . . . . . 6261,720 

1957 . . . . . . 4,254,764 .-. . . . . . . -.. . . . . . . .-. ..- -.. . . . . . . 

1958 . . . . . . 4,203,812 1,474 23,872 34,732 86,260 140,404 563,126 3,084,920 ..- . . . . . . 7247,024 

1959 . . . . . . 4,244,796 .-. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1960 . . . . . . 4,257,650 1,656 24,154 34,210 93,726 132,370 640,114 3,087,898 . . . . . . . . . 7243,722 

1961 . . . . . . 4,266.326 -.. .-. . . . -.. . . . -.. .-. . . . . . . 

1962 . . . . . . 4,167,362 1,726 23,606 33,008 92,378 120,388 538,298 3,016,834 . . . . . . 7241,120 

1963 . . . . . . 4,096,020 I,306 22,544 31,516 89,788 113,252 622,154 2,935,222 .-. ..- . . . 7282,228 

1964 . . . . . . 4,027,490 942 22,328 31,498 92,306 112,836 550,852 2,665,422 2,539,606 275,486 50,330 7251,206 

1965 . . . . . . 3,760,358 810 20,514 28,150 85,952 102,654 502,324 2,664,518 Z,341 ,376 272,916 50,226 7254,436 

1966 . . . . . . 3,606,274 752 19,728 27,758 82,590 98,060 579,406 2,548,096 ?,227,166 270,410 50,518 7249,862 

1967 . . . . . . 3,520,959 652 18,304 26,478 80,637 93,821 571,062 2,471,844 ?,142,988 274,739 54,217 7257,861 

White 

1950 . . . . . . ‘ 3,063,627 505 14,896 ?3,853 55,321 197,907 Z48,387 ?,279,922 !,175,874 91,750 12,296 2241,726 

1951 . . . . . . 3,237,072 540 16,260 ?3,966 55,286 177,494 ?69,1368 !,484,282 !,360,974 108,164 14,124 3210,356 

1952 . . . . . . 3,322,658 554 I 5,756 !4,242 57,360 147,906 113,440 !,527 ,200 !,375,624 151 76 4236,198 

1953 . . . . . . 3,356,772 620 16,308 !3,460 56,530 I 35,490 108,716 !,598,288 !,433,032 165 56 ‘217,360 

1954 . . . . . . 3,443,630 -.. . . . . . . . . . .-. . . . . . . -.. . . . . . . 

1955 . . . . . . 3,458,446 . . . . . . . . . ..- . . . -.. . . . ..- . . . -.. . . . 

1956 . . . . . . 3,545,350 876 17,266 23,946 60,800 118,656 394,712 2,691,598 . . . . . . . . . 6237,596 

1957 ...,.. 3,621,456 . . . -.. ..- . . . . . . -.. ..- . . . . . . . . . 

1958 . . . . . . 3,572,306 966 17,656 25,064 67,954 105,764 501,118 2,634,000 . . . .-. -.. 7219,762 

1959 . . . . . . 3,597,430 . . . . . . ..- . . . -.. ..- . . . . . . . . . . . . 

1960 . . . . . . 3,600,744 1,056 17,432 24,102 71,342 99,508 549,198 2,619,812 . . . . . . . . . 7218,294 

1961 . . . . . . 3,600,664 . . . . . . . . . . . . .-. . . . . . . . . . . . . . . . . . . 

19628 . . . . . 3,384,068 1,164 16,284 22,338 67,454 87,110 525,6& 2,458,900 . . . -.. 7215,134 

19638 . . . . . 3,326,344 

1964 . . . . . . 3,369,160 

1965 . . . . . . 3,123,660 

1966 . . . . . . 2,993,230 

1967 . . . . . . 2,922,502 

All other 

1950 . . . . . . ‘490,522 

1951 . . . . . .. 513,778 

1952 . . . . . . 524,328 

1953 . . . . . . 545,348 

1954 . . . . . . 573,732 

1956 . . . . . . 588,847 

1956 . . . . . . 617,740 

1957 . . . . . . 633,326 

1956 . . . . . . 631,506 

1959 . . . . . . 647,366 

See footnotes at end of table. 

754 15,306 21,382 65,738 81,772 512,024 Z,364,584 . . . . . . 7244,784 

622 15,070 21,466 68,162 83,096 550,836 ?,407,682 ?,114,636 249,368 43,478 7222,236 

506 14,002 19,594 63,314 76,130 XYI,360 ?,225,426 I,935,774 246,222 43,430 7221,526 

478 13,164 18,616 60,464 71,756 !64,116 1,128,072 1,840,822 243,808 43,442 7216,674 

420 12,055 17,625 59,102 69,021 !75,721 ?,065,080 1,770,029 248,291 46,760 7223,477 

141 3,443 6,161 9,291 50,262 29,219 338,687 331,973 5,571 1,143 252,853 

144 3,790 6,650 10,408 48,826 33,874 382,736 374,690 6,534 1,312 327,250 

178 4,1 ‘Jo 7,126 11,166 41,368 40,392 398,436 389,316 9, !2 421,550 

236 4,336 7,602 11,780 36,636 44,722 423,348 411,924 11, !4 s 16,664 

. . . . . . . . . . . . . . . .-. . . . . . . . . . 

. . . -.. . . . -.. .-. . . . . . . . . . ..- .-. . . . 

332 5,826 6,616 16,124 39,676 60,904 461,936 ..- . . . . . . ‘24,1 24 

. . . . . . . . . ..- -.. .-. . . . -.. ..- . . . . . . 

506 6,216 9,666 20,306 34,640 82,006 450,920 . . . . . . . . . 727,242 

. . . . . . . . . . . . . . . . . . .-. ..- ..- .-. . . . 

34 
--- --- ---

---

I 

Table 1. Number of live births by period of gestation and color: United States, 1950-67-Con. 

f 

Period of gestation (weeks) 

Year and 

color Under 40 and 43 and Not Total 20 20-27 28-31 32-35 36 37-39 over 40 41J12 over stated 

AL! 

gther-Con. 

1960 . . . . . . 667,106 600 6,722 10,108 22,384 32,862 90,916 468,086 ..- . . . -.. 725,428 

1961 . . . . . . 667,462 . . . . . . . . . .-. ..- . . . .-. . . . 

19628 . . . . . 641,580 506 6,616 9,662 22,186 30,644 94,306 452,676 . . . . . . 725,082 

19638 ..,.. 638,928 490 6,500 9,172 21,332 28,702 91,374 444,668 . . . -.. .-. 736,690 

1964 . . . . . . 658,330 320 7,258 10,042 24,144 29,840 100,016 457,740 424,770 26,118 6,852 728,970 

1966 . . . . . . 636,498 302 6,512 9,556 22,638 27,524 97,964 439,092 405,602 26,694 6,796 732,810 

1966 . . . . . . 613,044 274 6,574 9,142 22,126 26,324 95,292 420,024 386,346 26,602 7,076 733,288 

1967 .,.... 596,457 232 6,248 8,853 21,735 24,800 95,341 406,864 372,959 26,448 7,457 734,384 

,1 Includes a number of live births 

1 Includes all live births recordad 

a Includes all live births recorded 

~ Includes all live births recorded 

s Includes all live birtha recorded 

6 I ncludea all live births recordad 

7 Includes all Iiva births recordad 

classified as premature with gestation not specified: total-1 ,555, whita—1,1 10, and othar445. 

in Louisiana and Massachusetts. 

in Massachusetts. 

in Massachusetts and practical y all of those recorded in Washington. 

in Massachusetts and Washington. 

in Maryland outside Baltimore, Massachusetts and Washington. 

in Maryland outside 8altimore, and Massachusetts. 

a Figures by color axcluded for New Jersey. 

35 
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---

---

---

---

---

---

---

---

---

---

---

---

---

---

Table 2. Percentage distribution of live births by period of gestation and color: United States, 1950-87 

[Data for the years 1951-54 and 1956-66 are based on a 50-percant sample of births; data for 1967 are based on a 20- to 50-percent 

sample] 

Period ofgestation (weeks) 

Year and 

color 

Total 

19501 . . . . . . . . . . . . . 

19512 . . . . . . . . . . . . . 

19523 . . . . . . . . . . . . . 

19534 . . . . . . . . . . . . . 

1954 . . . . . . . . . . . . . . 

1955 . . . . . . . . . . . . . . 

19565 . . . . . . . . . . . . . 

1957 . . . . . . . . . . . . . . 

19586 . . . . . . . . . . . . . 

1959, . . . . . . . . . . . . . 

19606 . . . . . . . . . . . . . 

1961 . . . . . . . . . . . . . . 

19626 . . . . . . . . . . . . . 

19636 . . . . . . . . . . . . . 

19646 . . . . . . . . . . . . . 

19656 . . . . . . . . . . . . . 

19666 . . . . . . . . . . . . . 

19676 . . . . . . . . . . . . . 

White 

19501 . . . . . . . . . . . . . 

19512 . . . . . . . . . . . . . 

19523 . . . . . . . . . . . . . 

19534 . . . . . . . . . . . . . 

1954 . . . . . . . . . . . . . . 

1955 . . . . . . . . . . . . . . 

19565 . . . . . . . . . . . . . 

1957 . . . . . . . . . . . . . . 

19586 . . . . . . . . . . . . . 

1959 . . . . . . . . . . . . . . 

19606 . . . . . . . . . . . . . 

1961, . . . . . . . . . . . . . 

19626’7 . . . . . . . . . . . 

19636’7 . . . . . . . . . . . 

19646 . . . . . . . . . . . . . 

19666 . . . . . . . . . . . . . 

19666 . . . . . . . . . . . . . 

19676 . . . . . . . . . . . . . 

Under 37 and Under 40 and 43 and 

Total 28-31 32-35 36 37-39 40 41-42 

37 over 28 over over 

100.0 11.1 86.9 0.6 0.9 2.0 7.6 8.5 80.4 76.9 3.0 0.4 

100.0 9.7 90.3 0.6 0,9 1.9 6.4 8,6 81.6 77.9 3.3 0.4 

100.0 8.6 91.4 0.6 0.9 1.9 5.3 9.9 81.5 77.0 4,5 

100.0 8.o 92.0 0,6 0.8 1.9 4.7 9.6 82.4 77.6 4.8 

100.0 ..- . . . -.. .-. -.. ..- . . . .-. -.. 

100.0 . . . -.. -.. -.. . . . . . . . .. . . . . . . . . . . . . 

100.0 7.5 92.5 0.6 0.8 2.0 4,1 11.7 80.8 . . . . . . . . . 

100.0 . . . -.. ..- ..- -.. . . . . . . . . . 

100.0 7.3 92.7 0.6 0.9 2.2 3.5 14.7 78.0 ..- . . . . . . 

100.0 . . . . . . -.. .-. -.. . . . . . . . . . 

100.0 7.1 92,9 0.6 0.9 2.3 3.3 15.9 76.9 -.. . . . .-. 

100,0 . . . . . . -.. . . . . . . -.. . . . . . . . . . 

100.0 6.$1 93.1 0.6 0.8 2.4 3.1 16.3 76.8 . . . -.. . . . 

100.0 6.8 93.2 0.6 0.8 2.4 3.0 16.3 76.9 .-. . . . . . . 

100.0 6.9 93.1 0.6 0.8 2.4 3.0 17.2 75.9 67.3 7.3 1.3 

100.0 6.8 93.2 0.6 0.8 2.5 2.9 17.2 76.0 66.8 7.8 1.4 

100.0 6.8 93.2 0.6 0.8 2.5 2,9 17.3 75,9 66.4 8.1 1,5 

100.0 6.7 93.3 0.6 0.8 2.5 2.9 17.5 75.8 65.7 8.4 1.7 

100.0 10.4 88.6 0.5 0.8 2.0 7.0 8.8 80.8 77.1 3.3 0.4 

100.0 9.0 91.0 0.5 0.8 1.8 5.9 8.9 82.1 78.0 3.6 0.5 

100.0 8,0 92.0 0.5 0.8 1.9 4.8 10,2 81.9 77.0 4.9 

100.0 7,4 92.6 0.5 0,7 1.8 4.3 9.8 82.8 77.5 5.3 

100.0 . . . . . . ..- . . . -.. -.. . . . . . . . . . . . . 

100.0 . . . . . . . . . -.. . . . -.. . . . . . . . . . . . . 

100.0 6.7 93.3 0.5 0.7 1.8 3.6 11.9 81.4 . . . . . . . . . 

100.0 -.. .-. ..- . . . . . . . . . .-. . . . . . . . . . . . . 

100.0 6.5 93.5 0.6 0.7 2.0 3.2 14.9 78.6 . . . . . . . . . 

100,0 -.. .-. -.. -.. . . . . . . -.. ..- -.. . . . 

100.0 6.3 93.7 0.5 0.7 2.1 2.9 16.2 77.5 . . . . . . .-. 

100.0 . . . . . . ..- -.. -.. -.. .-. . . . 

100.0 6.1 93.9 0.5 0.7 2.1 2.7 16.5 77.3 . . . . . . . . . 

100.0 6.0 84.0 0.5 0.7 2.1 2.7 16.6 77.4 . . . . . . . . . 

100.0 6.0 84.0 0.5 0.7 2.2 2.6 17.5 76.5 67.2 7.9 1.4 

100.0 5.9 94.1 0.5 0.7 2.2 2.6 17,4 76.7 66.7 8.5 1.5 

100.0 5.9 84.1 0.5 0.7 2.2 2.6 17,4 76.6 65.3 8.8 1,6 

100.0 5.9 84.1 0.5 0.7 2.2 2,6 17.6 76.5 65.6 9.2 1,7 

See footnotes at end of table. 

36 
---

---

--- ---

---

Tabla2. Percentage distribution of Iivabirths byperiod ofgastation and color: United States, 1950-67-Con. 

Period of gestation (weak) 

Year and 

color Under 37 and Under 40 and 4142 43and Total 28-31 32-35 36 37-39 40 37 28 over over 

All other 

19501 . . . . . . . . . . . . . 100.0 15.9 &.1 0.8 1.4 2.1 11.5 6.7 77.5 75.9 -!-- 1.3 0.3 

19512 . . . . . . . . . . . . . 100.0 14.4 86.6 0.8 1.4 2.1 10.0 7.0 78.7 77.1 1.3 0.3 

19523 . . . . . . . . . . . . . 100.0 12.7 87.3 0.9 1.4 2.2 8.2 8.0 79.2 77.4 1.8 

19534 . . . . . . . . . . . . . 100.0 11.5 66.5 0.9 1.4 2.2 6.9 8.5 80.1 77.9 2.2 

1954 . . . . . . . . . . . . . . 100,0 . . . . . . . . . ..- -.. -.. .-. ..-

1955 . . . . . . . . . . . . . . 100.0 ..- . . . . . . -,- . . . .-. . . . -.. . . . ..- . . . 

19565 . . . . . . . . . . . . . 100.0 11.9 88.1 1.0 1.5 2.7 6.7 10.3 77.8 . . . . . . .-. 

1957 . . . . . . . . . . . . . . 100.0 . . . . . . . . . . . . . . . . . . ..- . . . -.. .-. 

19586 . . . . . . . . . . . . . 100,0 11.8 66.2 1.1 1.6 3.4 5.7 13.6 74.6 .-. ..-

1959 . . , , , , , . . , . , . . 100.0 . . . . . . -.. . . . -.. . . . . . . ..- . . . . . . -.. 

19606 . . . . . . . . . . . . . 100,0 11.5 88.5 1.2 1.6 3.5 5.2 14.4 74.1 ..- . . . ..-

1961, ,.. ,. .,,..... 100.0 . . . . . . . . . . . . -.. . . . . . . ..- . . . . . . -.. 

19626’7 . . . . . . . . . . . 100,0 11.3 88.7 1.2 1.6 3.6 5.0 15.3 73.4 ..- . . . . . . 

19636’7 , . . . . . . . . . . . 100.0 11.0 89.0 1.2 1.5 3.5 4.8 15.2 73.8 . . . -.. .-. 

19646 . . . . . . . . . . . . . 100.0 11.4 88.6 1.2 1.6 3.8 4.7 15.9 72.7 67.5 4.1 1.1 

19656 . . . . . . . . . . . . . 100.0 11.0 89.0 1.1 1.6 3.8 4.6 16.2 72.7 67.2 4.4 1.1 

19666 . . . . . . . . . . . . . 100.0 11,1 88.9 1.2 1.6 3.8 4.5 16.4 72.4 66.6 4.6 1.2 

19676 . . . . . . . . . . . . . 100.0 11.0 89,0 1.1 1.6 3.9 4.4 16.9 72.1 66.1 4.7 1.3 

*Excludes all Iivebirths racordadin Louisiana and Massachusetts, 

aExcIudes all Iive births recorded in Massachusetts. 

‘Excludes all live births racorded in Massachusetts and practically all those recorded in Washington. 

‘Excludes all live births recordad in Massachusetts and Washington. 

‘Excludes all live tirthsrecorded in Maryland outsida Baltimore, Massachusettsand Washington. 

cExcludes all live births recorded in Maryland outsida Baltimore and Massachusetts, 

T Figures by color excludad for New Jaw37 
Tabla3. Number oflivebirtha by birth weight and color: United States, 1950-57 

[Data for the years 1951-54 and 1956-66 are based on a 50-percent sample of bkths; data for 1967 are based on a 20- to 50-percent sampIe] 

Birth weight (grams) 

1950 . . . . . . 3,564,149 14,114 19,926 46,441 168,571 607,855 1,259,213 892,047 24B,949 

T

1233,349 

1951 . . . . . . 3,750,650 15,344 20,984 49,360 180,640 647.280 1,348,438 948,646 261,624 54,856 I 7,348 ‘216,130 

1952 . . . . . . 3,846,986 16,616 22,062 51,428 164.878 669,786 1,390,776 976,272 266,834 61,706 ‘ 206,528 

1953 . . . . . . 3,902,120 17,640 22,870 52,664 188,046 685,542 1,415,034 995,644 272,668 61, 12 1190,680 

1954 . . . . . . 4,017,362 18,670 23,276 53,056 188,990 698,854 1,460,746 1,034,626 284,360 55,908 7,466 1191,306 

1955 . . . . . . 4,047,295 19,606 24,151 54,252 193,769 711,174 1,472,159 1,036,673 285,258 54,750 7,248 1188,053 

1956 . . . . . . 4,163,090 20,328 24,566 55,884 200,076 733,562 1,524,102 1,073,064 297,880 55,416 7,148 2171,062 

1957 . . . . . . 4,254,784 21,126 25,892 56,378 206,982 763,008 1,573,570 1,102~52 301,822 55,330 7,028 3137,296 

1958 . . . . . . 4,203,812 21,810 25,620 58,612 207,496 756,742 1,553,222 1,085,574 299,024 54,856 6,790 3134,064 

1959 . . . . . . 4,244,796 23,164 27,058 61,394 215,178 784,394 1,608,404 1,128,554 312,406 57,196 7,196 19,852 

1960 . . . . . . 4,257,850 23,006 26,928 61,266 216,282 784,200 1,511,358 1,135,522 316,808 5832 7,440 16,696 

1961 . . . . . . 4,268,326 22>46 27,128 62,196 220,696 800,762 1,621,374 1,125,184 308,810 56,602 7,176 14,452 

1962 . . . . . . 4,167,362 23,404 26,844 62,412 219,398 796,350 1,585,576 1,084,486 294,588 53,668 7,106 13,530 

1963 . . . . . . 4,086,020 22,714 26,882 62,526 220,968 791,078 1,559,694 1,054,014 284,104 50,634 6,242 18,964 

1964 . . . . . . 4,027,490 22,355 26,760 61 S186 218,430 775,682 1,536,768 1,037,702 280,630 50,896 6,500 9,780 

1965 . . . . . . 3,760,356 21,238 24,938 58,458 206,380 735,894 1,437,358 958,634 255,630 46,182 5,968 8,478, 

1966 . . . . . . 3,606,274 19,980 24,688 56,650 199,036 713,464 1,382,170 913,296 240,870 42,384 5,562 8,074 

1967 . . . . . . 3,520,959 19,205 23,536 54,836 190J325 692,558 1,352,533 696,627 238,323 40,933 5,451 8,132 

Year and 

color Total 

1,000 1,oo1- 1,501- 2,001- 2,501- 3,001- 3,501- 4,001- 4,501- 5,001 Not 

or 

lass 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 ‘r steted more 

Total — 

63,682 

w1950 . . . . . . 3,063,627 11,482 15,855 37,478 137,195 509,521 1,086,735 787,507 217,336 48$ )5 ‘201/812 

1951 . . . . . . 3,237,072 12,288 16,352 39,526 146,064 540,820 1,173,378 636,364 229,256 43,296 6,120 1192,488 

1952 . . . . . . 3,322,658 13,160 17,300 40,952 147,666 556,634 1,209,020 666,814 235,584 46; ;0 1186$348 

1953 .,.... 3,356,772 13,918 17,588 41,354 148,880 564,968 1,222,502 882,642 240,792 49; ;6 ‘ 174,952 

1954 . . . . . . 3,443,630 14,260 17,582 41,048 148,008 569,876 1,256,314 916,536 252,482 45,906 5,6& 1175,932 

1955 . . . . . . 3,458,448 14,936 18,183 41,397 150,352 574,803 1,261,345 918,329 253,812 45,728 5,687 ‘ 173,875 

1956 . . . . . . 3,545,350 15,094 16,244 42,354 152,868 589,354 1,300,484 950,856 266,082 46916 5,542 2157,436 

1957 . . . . . . 3,621,456 16,440 19,070 43,778 158,626 610,588 1,342,020 980,368 271,654 47,412 5s12 3126,738 

1958 . . . . . . 3,672,306 16,050 18,490 43,204 155,828 601,372 1,322,590 966,6S4 270,0@3 47,772 5,708 3124,600 

1959 . . . . . . 3,597,430 16,762 19,738 45,294 161,850 622,122 1/370,004 1,007,176 283,672 49974 6,150 14,668 

1960 . . . . . . 3,600,744 16,630 19,484 45,234 162,402 619,200 i,369,022 1,012,080 266,878 51 /366 6,380 12,058 

1961 . . . . . . 3,600,864 16,426 19,56a 45,582 165,060 632,046 1,374,184 1,001,222 280,440 49,760 6,178 10,348 

19624 . . . . . 3,394,068 16,216 16,6W 44,200 158,930 606,846 1,297,174 932,696 257,936 45,886 5,884 9,490 

19634 . . . . . 3,326,344 15,392 18,458 43,596 158,516 600,448 1,273J22 905,258 249,056 43,662 5,218 13,418 

1964 . . . . . . 3,369,160 15,320 18,632 44,386 160,336 604,494 1,293,664 920,384 254,286 45,024 5,606 7,008 

1965 . . . . . . 3,123,860 14,362 17,284 41,522 150,492 569,890 1,200,838 845,758 231,802 40,734 5,094 6,064 

1966 . . . . . . 2,993,230 13,326 16,870 40,302 145,222 551,166 1,154,786 805,604 217,726 37,752 4,752 5,824 

1967 . . . . . . 2,922,502 12,741 16,087 39,017 139,562 534,827 1,129,124 790J80 213,515 36,466 4,633 6,050 

All other 

1950. .,... 490,522 2,632 4,073 8,963 31,376 98,334 162,478 ‘f04,540 31,613 15J 16 ‘ 31,437 

1951 . . . . . . 513,778 3,056 4,632 9,834 34,756 106,360 175,060 110,282 32,368 11,580 2,228 123,642 

1962 . . . . . . 524,328 3,456 4,762 10,476 37,192 113,152 181,756 109,458 31,350 12; 16 119J380 

1953.. ,... 545,348 3,722 5,282 11,310 38,366 120,554 192,532 113,002 31,876 11;‘6 115,726 

1954 . . . . . . 573,732 4,410 5,696 12,006 40,962 129,076 204,432 118,090 31,878 10,002 1,782 ] 15,376 

/ 

1955 . . . . . . 588,847 4,872 5,968 12,855 43,477 136,371 210,814 118344 31,446 9,021 I,ml 114,178 

1956 . . . . . . 617,740 5,234 6,322 13,530 47,210 144,206 223,606 122,208 31,788 8,500 1,506 213,626 

1957 . . . . . . 633,328 5,666 6,822 14,660 50,356 152,420 231,550 121j884 30,158 7,918 1,216 310,558 

1958 . . . . . . 631,506 5,760 7,130 15,406 51,668 155,370 230,632 118,890 29,016 7,086 1,082 39,464 

1959 . . . . . . 647,366 6,402 7,320 16,100 53,328 162,272 238,400 121j378 28,734 7,222 1,046 5,164 

See footnotes at end of table. 

38 
Table 3. Number of live births by birth weight and color: United States, 1950%7-Con. 

- n 

8irth weight (grams) 

Year and 

color 

Total 

1,000 1,oo1- 1,501- 2,001- 2,501- 3,001- 3,501- 4,001- 4,501- 5,001 Not or or 

less 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 stated 

~ 

other-Con. 

1

II 

1960 ,, ..,, 657,106 6,378 7,434 16,032 53,880 165,000 242,336 123,442 29,930 6,976 1,060 4,638 

1961 . . . . . . 667,462 6,520 7,540 16,614 55,606 168,716 247,190 123,962 29,370 6,842 998 4,104 

19624 ...,. 641,560 6,370 7,456 16,248 53,540 183,680 237,458 118,142 27,922 6,210 1,024 3,530 

19634 .,.,. 636,928 6,480 7,672 16,934 55,226 164,196 235,238 115,226 26,302 5,678 848 5,128 

1964 . . . . . . 658,330 7,036 8,128 17,600 58$94 171,188 243,084 117,318 26,344 5,872 894 2,772 

1965 . . . . . . 636,496 6,856 7,664 16,936 55,888 166,004 236,520 113,076 24,828 5,448 874 2,414 

1966 . . . . . . 613,044 6,654 7,818 16,348 53,814 162,298 227,384 107,792 23,244 4,632 810 2,250 

1967, . . . . . 598,457 6,464 7,449 15,819 51,263 157,631 223,409 106,247 22,808 4,467 818 2,082 

1Includes all live births recordad in Massachusettsand Connecticut. 

21ncludes all live Mrthsrecorded in Massachusettsforentire year and Connecticut for part of year. 

31ncludes all Iive births recorded in Massachusetts. 

a Figures by color excluded for New Jersey. 

39 
Table 4. Percentage distribution of live births by birth weight and color: United States, 1950437 

[Data for the years 1951-54 and 1956-66 ue based on a 50-percent sasnple of births; data for 1967 are based on a 20- to 50-percent 

sasnple] 

8irth weight (grams) 

19501 

19511 . 

., 

. 

. 

. 

100.0 

100.0 

7.5 

7.5 92.5 

92.5 

0.4 

0.4 

0.6 

0.6 

1.4 

1.4 5.1 

5.1 18.3 

18.3 37.9 

38.1 

26.9 

26,8 7.4 

7.5 

T

1.6’19 0,2 

19521 . . . 100,0 7.6 92.4 0.5 0.6 1.4 5.1 18.4 38,2 26.8 7.3 1.7 

19531 . . . 100,0 7.6 92.4 0.5 0.6 1.4 5.1 18.5 38.1 26.8 7.3 1 

19541 . . . 100.0 7.4 92.6 0.5 0.6 1.4 4.9 18.3 36.2 27.0 7.4 1,5 0,2 

19551,.. 100.0 7.6 92.4 0.5 0.6 1.4 5.0 18.4 38.1 26.9 7.4 1,4 0.2 

19562 . . . 100.0 7.5 92.4 0.5 0.6 1.4 5.0 18.4 38.2 26.9 7,5 1.4 0.2 

19573,. . 100,0 7.6 92.4 0.5 0.6 1.4 5.1 18.5 38.2 26.8 7.3 1.3 0.2 

19583 . . . 100.0 7.7 92.3 0.5 0.6 1.4 5.1 18.6 38.2 26.7 7.3 1.3 0.2 

1959 . . . . 100.0 7.7 92.3 0.5 0.6 1.5 5.1 18.6 38.1 26.7 7.4 1.4 0.2 

Year and 

color Total 

2,500 2,501 1,000 1,oo1- 1,501- 2,001- 2,501- 3,001- 3,501- 4,001- 4,501- 5,001 

or or or 

less more less 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 ‘r more 

Total 

1960 . . . . 100.0 7.7 92.3 0.5 0.6 1.4 5.1 18.5 38.0 26.8 7.5 1.4 0,2 

1961 . . . . 100.0 7.8 92.2 0.5 0.6 1.5 5.2 18.8 38.1 26.5 7.3 1.3 0.2 

1862 .,.. 100.0 8.0 92.0 0.6 0.6 1.5 5.3 19.2 36.2 26.1 7.1 1.3 0,2 

1963 ..,, 100.0 8.2 91.8 0.6 0.7 1.5 5.4 19.4 38.2 25.8 7.0 1.2 0.2 

1964 ..., 100.0 8.2 91.8 0.6 0.7 1.5 5.4 19.3 38.2 25.8 7.0 1.3 0,2 

1965 . . . . 100.0 8.3 91.7 0.6 0.7 1.6 5.5 19.6 38.3 25.6 6.8 1.2 0.2 

1966 . . . . 100.0 8,3 91,7 0.6 0.7 1.6 5.5 19.8 38.4 25.4 6,7 1.2 0.2 

1967 . . . . 100,0 8.2 91.8 0.5 0.7 1.6 5.4 19.7 38.5 25.5 6.7 1.2 0.2 

White 

1950’ . . . 100.0 7.1 92.9 0.4 0.6 1.3 4.8 17.8 38.3 27.5 7.6


19511 . . . 100.0 7.0 93.0 0.4 0.5 1.3 4.8 17.8 38.5 27.5 7.5 1.4’i7 0.2


19521 . . . 100.0 7.0 93,0 0,4 0.6 1.3 4.7 17.7 38.6 27.6 7,5 1.6


19531 . . . 100.0 7.0 93.0 0.4 0.6 1.3 4.7 17.8 38.4 27.7 7.6 1,6


1954’ . . . 100.0 6.8 93.2 0.4 0.5 1.3 4.5 17.4 38.4 28.0 7.7 1.4 0,2


19551 . . . 100.0 6.8 93.2 0.5 0.6 1.3 4.6 17.5 38.4 28.0 7.7 1.4 0,2


19562, ., 100.0 6,7 93.3 0.4 0.5 1.3 4.5 17.4 38.4 28.1 7,9 1.4 0.2


19573 . . . 100.0 6.8 93.2 0.4 0,5 1.3 4.5 17.5 38.4 28.1 7.8 1.4 0.2


19583 . . . 100.0 6.8 93.2 0.5 0.5 1.3 4.5 17.4 38.4 28.0 7.8 1.4 0.2


1959 . . . . 100.0 6.8 93.2 0.5 0.6 1.3 4.5 17.4 38.2 28.1 7.9 1.4 0,2


1960, .,. 100.0 6.8 93.2 0.5 0.5 1.3 4.5 17,3 38.1 28.2 8,0 1.4 -0.2


1961 . . . . 100.0 6.9 93.1 0.5 0.5 1.3 4.6 17.6 38.3 27.9 7.8 1.4 0.2


19624 . . . 100.0 7.0 93.0 0.5 0.5 1.3 4.7 17.9 38.3 27.6 7.6 1.4 0.2


19634 . . . 100.0 7.1 92.9 0.5 0.6 1.3 4,8 18.1 38.4 27,3 7.5 1.3 0.2


1964 . . . . 100.0 7.1 92.9 0.5 0.6 1.3 4.8 18.0 38.5 27.4 7.6 1.3 0.2


1965 . . . . 100.0 7.2 92.8 0.5 0.6 1.3 4.8 18.3 38.5 27.1 7.4 1.3 0.2


1966 ..,. 100.0 7.2 92.8 0.4 0.6 1.3 4.9 18.4 38.7 27.0 7,3 1,3 0.2


1967 . . . . 100.0 7,1 92.9 0.4 0.6 1.3 4.8 18.3 38.7 27.1 7.3 1.3 0.2


see footnotes at end of table. 

40 
I 

Tabla4. PercanWge distribution oflive Mrthsby tirthweight and color: United States,1950-S7-Con. 

8irth weight (grams) 

I Year and 

I color Total 

2,500 2,501 1,000 1,oo1- 1,501- 2,001- 2,501- 3,001- 3,501- 4,001- 4,501- 5’W’ or or or 5,000 less more less 1,500 2,000 2,500 3,000 3,500 4,000 4,500 T M:re 

All other 

1950’ ,,, 100.0 10.2 89.8 0.6 0.9 2.0 6.8 21.4 35.4 22.8 6.9


T


19511 . . . 100.0 10.7 89.3 0.6 0.9 2.0 7.1 21.7 35.7 22,5 6.6 2.43i3 0.5


19521 .,, 100.0 11.1 88.9 0,7 0.9 2.1 7.4 22.4 36.0 21.7 6.2 2,5


19531 .,. 100.0 11.3 88.7 0.7 1.0 2.1 7.4 22.8 36.4 21.3 6.0 2.3


19541 .,. 100.0 11.3 88.7 0.8 1.0 2.2 7.3 23.1 36.6 21.1 5.7 1.8 0.3


19551 .,. 100.0 11.7 88.3 0.8 1.0 2.2 7.6 23,7 36.7 20,6 5.5 1.6 0.3


19562, ,, 100,0 12.0 88.0 0.9 1.0 2.2 7.8 23.9 37.0 20.2 5.3 1.4 0.2


19573,,, 100!0 12,4 87.6 0.9 1.1 2.4 8.1 24.5 37.2 19.6 4.8 1.3 0.2


19583,. . 100.0 12.9 87.1 0.9 1.1 2.5 8.3 25.0 37.1 19.1 4.7 1.1 0.2


1959 . . . . 100.0 12.9 87.1 1.0 1.1 2.5 8.3 25.3 37.1 18.9 4.5 1.1 0.2


1960,,,, 100,0 12,8 87.2 1.0 1.1 2.5 8.3 25.3 37.1 18.8 4.6 1.1 0.2


1961, ,,. 100.0 13.0 87.0 1.0 1.1 2.5 8.4 25.4 37.3 18.7 4.4 1.0 0,2


19624, ,. 100.0 13.1 86.9 1.0 1.2 2.5 8.4 25.7 37.2 18.5 4.4 1.0 0.2


19634 . . . 100.0 13.6 86.4 1.0 1.2 2.7 8.7 25.9 37.1 18.2 4.1 0.9 0.1


1964 ...,. 100.0 13.9 86.1 1.1 1.2 2.7 8.9 26.1 37.1 17.9 4.0 0.9 0.1


1965 ..,, 100.0 13,8 86.2 1.1 1.2 2.7 8.8 26.2 37.3 17.8 3.8 0.9 0.1


1966 ..,. 100.0 13.9 86.1 1.1 1.3 2.7 8.8 26.8 37.2 17.6 3.9 0:8 0.1


1967, ,,. 100.0 13.6 86.4 1,1 1.2 2.7 8.6 26.4 37.5 17.8 3.8 0.7 0.1


‘Excludes all Iive births recorded in Connecticut and Massachusetts.


2Excludes all live births recorded in Massachusettsforentirevear and Connecticut foroertof vear.


‘Excludesell Iive births recorded in Massachusetts.


4 Figures by color excluded for New Jersey.


41

Table5. Number of Iivebirths andpercentege distribution bycolor, Wrthweight, andwriod ofgestetion forareas reporting LMPandfor ereasreporting peri0rl 

0f9estati0n: United States, 1967 

lData are baaedon a 20- to 50-percent ample] 

Area and period Total 2,500 gramsor less 2,501 gramsm more Total 2,500 grams 2,501 grams or less or mom 

of gestation ZELz Jm-.L!& E12z 

All areas Jumber of live births Pe ,entagedistribution 

Total . . . . . . . . . . . . . . . . . 2,694,921 $62,63, 189,067 75,527 2,505,854 187,107 100.0 I 00.0 I00.0 100.0 100.0 100.0 — — . 

Under 37weaks . . . . . . . . . . . 157,204 61,412 92,601 38,449 64,703 22,963 5.8 10.9 48.9 50.9 2.6 4.7 

37weeks and over . . . . . . . . . 2.537,777 501,22: 96,566 37,076 2,441,151 454,144 94.2 89.1 51.1 49.1 97.4 95.3 

Under 28weeks . . . . . . . . . . . . . . 12,119 6,2W 11,621 5,959 498 323 0.4 1.1 6.1 7.9 0.0 0.1 

28-31 weeks . . . . . . . . . . . . . . . . . 17,4C8 8,755 15,658 7,785 1,750 974 0.6 1.6 8.3 10.3 0.1 0.2 

32-35 weeks . . . . . . . . . . . . . . . . . 58,799 21 ,6H 39,813 14,600 18,886 7,063 2.2 3.9 21.1 19.3 0.8 1.4 

36weeks . . . . . . . . . . . . . . . . . . . 68,878 24,70[ 25,408 10,105 43,469 14,603 2.6 4.4 13.4 13.4 1.7 3.0 

37-39 weeks . . . . . . . . . . . . . . . . . 475,113 95,171 44,756 13,446 430,357 81,725 17.6 16.9 23.7 17.8 17,2 !6,8 

40weaks . . . . . . . . . . . . . . . . . . . 1,767,885 372,18f 46,869 22,116 1,720,996 65.6 66.2 24.8 29.3 68.7 71.9 

4142 weeks . . . . . . . . . . . . . . . . . 248,035 26,41( 3,869 1,060 244,146 25,350 9.2 4.7 2.1 1.4 9.7 5.2 

43weeks and over . . . . . . . . . . . . 46,684 7,45! 1,032 456 45,652 6,999 1.7 1.3 0.5 0.6 1.8 1.4 

Total . . . . . . . . . . . . . . . . 413,466 88,98( 27,801 11,585 385,665 77,401 100.0 1Oo.c 100.0 100.0 100.0 100,0 

Under 37 weeks . . . . . . . . . . 34,929 16,1K 14,159 6,750 20,770 8,393 8.4 17.0 50,9 58,3 5.4 10,8 

37weeks and over . . . . . . . . 378,537 738S4: 13,642 4,835 364,895 69,008 91.6 83.0 49.1 41.7 94.6 89.2 

Undar28weaks . . . . . . . . . . . . . . 2,078 1,46[ 1,761 1,182 317 284 0.5 1.6 6,3 10.2 0.1 0,4 

28-31 weeks . . . . . . . . . . . . . . . . . 3,679 2,04 2,566 1,375 993 667 0.9 2.3 9.3 11.9 0.3 0.9 

32-35 weeks . . . . . . . . . . . . . . . . 16,946 7,3Q 7,212 3,079 9,734 4,223 4.1 6.2 25.9 26.6 2.5 5,5 

L%weeks . . . . . . . . . . . . . . . . . . 12,328 4,33 2,600 1,114 9,726 3,219 3,0 4.9 9.4 9.6 2.5 4.2 

37-39 weeks . . . . . . . . . . . . . . . . 158,344 36,97: 9,260 3,113 147,084 33,860 37.8 41.5 33.3 26.9 38.1 43.7 

40weeks . . . . . . . . . . . . . . . . . . 97,723 16,79 2,062 739 95,661 16,053 23.6 18.9 7.4 6.4 24.8 20.7 

4142weeks . . . . . . . . . . . . . . . . 96,945 14,55: 1,644 611 95,301 13,942 23.4 16.4 5.9 5.3 24.7 18.0 

43weaks Andover . . . . . . . . . . . 27,525 5,52! 676 372 26,S49 5,153 6.7 6.2 2.4 3.2 7.0 6.7 

Areas reporting 

gestetionperiod 

Total . . . . . . . . . . . . . . . . . ?,281,455 173,641 161,266 63S42 2,120,189 !09,706 100.0 I00.0 100.0 100.0 100.0 OQ.o 

Under 37weeks . . . . . . . . . . . 122,275 46,26! 78,342 31,699 43,833 14,570 5.4 9.8 48.6 49.6 2.1 3.6 

37 weeks and over . . . . . . . . . 2,159,180 127,37! 82,924 32,243 2,076,256 395,136 94.6 90.2 51.4 50.4 97.9 96.4 

Under 28weeks . . . . . . . . . . . . . . 10,O4I 4,81( 9,860 4.777 161 39 0.4 1.0 6.1 7.5 0.0 0.0 

28-31 weaks . . . . . . . . . . . . . . . . . 13,829 6,71’ 13,072 6,410 757 307 0.6 1.4 8.1 10.0 0.0 0.1 

32-35 waeks . . . . . . . . . . . . . . . . . 41,653 14,36 32,601 11,521 9,252 2,840 1.8 3.0 20,2 18.0 0.4 0.7 

36weeks . . . . . . . . . . . . . . . . . . . 56,552 20,37’ 22,808 8,991 33,743 11,384 2.5 4.3 14.1 14.1 1.6 2.8 

37-39 weeks . . . . . . . . . . . . . . . . . 318,769 58,19 35,496 10,333 283,273 47,865 14.0 12.3 22.0 16.2 13,4 11.7 

40weeka . . . . . . . . . . . . . . . . . . . 1,670,162 155,39 44,627 21,377 1,625,335 334,017 73.2 75.0 27.8 33.4 76.7 61.6 

41-12 weeks . . . . . . . . . . . . . . . . . 151,090 11,65 2,245 449 148,645 11,408 6.6 2.5 1.4 0,7 7.0 2.8 

43waeks and over . . . . . . . . . . . . 19,159 1,93 356 84 18,803 1,846 0.8 0.4 0.2 0.1 0.9 0.5 — 

1Flguras by period of gastation for these areas are based on an item on the birth record, first day of Iaat normal menstrual period (LMP). Areas included are 

Baltimore, California, District of Columbia, Minnesota, and New York City. 

42 
Table 6. Number of live births by age of mother and color: United Statas, 1950-67 

[Data for the years 19S 1-54 and 1956-66 are based on a 50-percent sample of births; data for 1967 are based on a 20- to 50-percent 

sample] 

Aga of mother (years) 

Year and 

color 

Total 

1950 . .,,.,.,,, 

1951 . . . . . . . . . . 

1952 . . . . . . . . . . 

1953 . . . . . . . . . . 

1954 ,,, .,,,,,, 

1955 . . . . . . . . . . 

1956 . . . . . . . . . . 

1957 . . . . . . . . . . 

1958 . . . . . . . . . . 

1959 . . . . . . . . . . 

1960 . . . . . . . . . . 

1961 . . . . . . . . . . 

1962 . . . . . . . . . . 

1963 . . . . . . . . . . 

1964 . . . . . . . . . . 

1965 . . . . . . . . . . 

1966 . . . . . . . . . . 

1967 . . . . . . . . . . 

w& 

1950 . . . . . . . . . . 

1951 . . . . . . . . . . 

1952 . . . . . . . . . . 

1953 . . . . . . . . . . 

1954 . . . . . . . . . , 

1955 . . . . . . . . . . 

1956 . . . . . . . . . . 

1957 . . . . . . , , . . 

1958 . . . . . . . . . . 

1959 . . . ,. . . . . , 

1960 . . . . . . . . . , 

1961 ,,, ,,.,,., 

19621 . . . . . . . . . 

19631 . . . . . . . . . 

1964 . . . . . . . . . . 

1965 . . . . . . . . . . 

1966 . . . . . . . . . . 

1967 ,, .,,..,.. 

Total Under 45 and Not 

15-19 20-24 25-29 30-34 35-39 4044 

15 over ,tated 

3,554,149 5,021 419,535 1,131,234 1,021/802 597,821 293,440 74,804 4,830 5,562 

3,750,850 5,086 443,872 1,198,966 1,072,374 637,238 304,898 78,224 4,932 5,260 

3,646,986 5,032 438,046 1,212,010 1,104,012 679,220 318/338 80,494 5,170 4,664 

3,902,120 5,316 455,878 1,220,532 1,110,768 691,080 326,102 83,290 5,004 4,140 

4,017,362 6,058 477,880 1,257,104 1,122,050 720,820 337,098 86,766 5,106 4,480 

4,047,295 5,883 484,097 1,273,908 1,119,279 722,277 3+5,305 87.587 5,111 3,648 

4,163,090 6,356 520,422 1,325,444 1,131,346 726,990 355,158 5,140 3,500 

4,254,784 6,960 550,212 1,361,396 1,140,806 730,818 365,298 90,808 5,272 3,214 

4,203,812 6,648 554,164 1,367,826 1,108,766 711,550 358,388 88,702 5,116 2,632 

4,244,796 6,776 671,048 1,406,200 l,099,6& 700,826 363,120 89,626 5,246 2,270 

4,257,850 6,780 586,966 1,426,912 1,082,816 687,722 359)808 91,564 5,182 . . . 

4,268,326 7,462 601,720 1,445,054 1,081,705 677,264 355,750 94,114 5,256 . . . 

4,167,362 7.340 600,298 1,444,978 1,045,086 638,382 334,708 91,490 5,080 . . . 

4,088,020 7,594 586,464 1,453,740 1,023$42 610,196 322,182 B8,982 4,930 . . . 

4,027,490 7,816 665,710 1,439,486 1,007,362 585,006 309J314 B7,626 4,670 . . . 

3,760,358 7,768 590,894 1,337,350 925,732 529,376 282$08 BI,716 4,614 . . . 

3,606,274 8,128 621,426 1,297,990 872,786 474,542 252,526 74,440 4,436 . . . 

3,520,959 8,593 596,445 1,310,588 867,426 439,373 227,323 57,053 4,158 . . . 

3,063,627 1,669 318,822 972,132 908,536 533,340 256,899 34S81 3,894 3,354 

3,237,072 1,718 ?40,670 1,035,310 951,422 567,102 266J42 ;7,370 4,036 3,102 

3,322,658 1,734 336,428 1,047,162 977,224 603,866 279,554 ;9,708 4,274 2,708 

3,356,772 1,854 350,984 J,O5I,91O 977,240 611,074 285,626 71,626 4,092 2,366 

3,443,630 2,172 367,812 1,079,944 982,894 634,776 294,010 74,968 4,252 2,802 

3,458,448 2,136 372,678 1,090,736 977,618 633,019 300,057 75,590 4,217 2,397 

3,545,350 2,348 402,822 1,132,460 986,014 631,974 307,178 77,156 4,278 2,120 

3,621,456 2,648 428,974 1,162,938 992,874 633,690 315$26 78,162 4,286 1,958 

3,572,306 2,648 432,696 1,169,056 961,896 615,300 308,808 76,268 4,178 1,456 

3.597,430 2,572 445,370 1,202,996 949,730 602,620 311,606 76,926 4,280 1,330 

3,600,744 2,524 458,130 1,219,962 942,112 588,402 307,426 77/876 4,212 . . . 

3,600,864 2,808 471,706 1,234,432 927,684 577,994 301,866 79~76 4,398 . . . 

3,394,068 2,690 459,832 1,197,864 863,124 520,260 271,476 74,752 4,070 . . . 

3,326,344 2,684 443,308 1,202,804 644,250 496,368 260/898 72,124 3,918 . . . 

3,369,160 2,676 444,358 1,224,876 864,784 494,714 260,634 73356 3,762 . . . 

3,123,860 2,444 $43,764 1,131,624 791,250 446,180 236,552 58,332 3,724 . . . 

2,993,230 2,666 165,112 1,101,120 749,226 399,368 210,706 31,452 3,560 . . . 

2,922,502 2,761 $35,239 1,116,686 749997 370,069 189J22 55,045 3,383 . . . 

Sea footnote at end of table. 

43 
Table 6. Number of live births by a% of mother and color: Unitad States, 1950-67-Con. 

Year and 

color 

All other 

1950 . . . . . . . . . .


1951 . . . . . . . . . .


1952 . . . . . . . . . .


1953 . . . . . . . . . .


1954 . . . . . . . . . .


1955 . . . . . . . . . .


1956 . . . . . . . . . .


1957 . . . . . . . . . .


1958 . . . . . . . . . .


1959 . . . . . . . . . .


1960 . . . . . . . . . .


1961 . . . . . . . . . .


19621 . . . . . . . . . .


19631 . . . . . . . . . .


1964 . . . . . . . . . .


1965 . . . . . . . . . .


1966 . . . . . . . . . .


1967 . . . . . . . . . .


Total


Under


15-19
 15


490,522 3,352 100,713 

513,778 3,388 103,202 

524,328 3,298 101,618 

545,348 3,462 104,894 

573,732 3,886 110,068 

568,847 3,747 111,419 

617,740 4,008 117,600 

633,328 4,312 121,238 

631,506 4,000 121,488 

647g366 4,204 125,678 

657,106 4,256 128/836 

667,462 4,654 130,014 

641,580 4,520 127,788 

638328 4,814 130,510 

658,330 5,140 141~52 

636,498 5,324 147,140 

613,044 5,462 156,314 

598,457 5,832 161,206 

Age of mother (years) 

$5 and Not


20-24 25-29 30-34 35-39 40-44
 over tated
 ---1 I


159,102 113S66 64,481 36,541 9fi23 936 2,208 

163,656 ; 120$)52 70,136 38,556 1oj354 896 2,158 

184,848 126,788 75,354 38,784 10,786 896 1,956 

168,622 133,528 80,016 40,476 11,684 912 1,774 

177,160 139,158 88,044 43,088 11,798 854 1,678 

183,172 141,661 89,258 45,248 11 #897 894 1,451 

192,9& 146,332 84,016 47,980 12,578 862 1,380 

198,458 147,932 97,128 49,372 12,646 986 1,256 

198,770 146,870 96,250 49,580 12,434 938 1,176 

203,204 149#854 98,206 51,514 12,700 966 940 

206,950 150,704 99,320 52,482 13,588 970 . . . 

210,622 154,022 99,270 53,884 14,138 858 . . . 

205,424 145,458 93,084 50,682 13,750 864 . . . 

207,712 142,762 89,836 48,744 13,676 874 . . . 

214,610 142,578 90,292 49,180 14,270 908 . . . 

205,726 134,482 83,196 46,356 13384 890 . . . 

196,870 123,560 75,174 41,820 12,988 856 . . . 

193,902 117,428 69,304 38,001 12,008 775 . . . 

i Figures by color excluded for New Jersey. 

44

Table 7. Percentage distribution of live births by age of mother and color: United States, 1950-S7 

[Data for the years 1951-54 and 1956-66 are based on a 50-percent sample of births; data for 1967 are based on a 20- to SO-percent 

sample] 

Age of mother (years) 

Year and 45 color Under 

Total 15-19 20-24 25-28 30-34 35-39 4044 and 15 over 

1950 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 11.8 31.9 28.8 16.8 8.3 2.1 0.1 

1951 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 11.9 32.0 28.6 17.0 8.1 2.1 0.1 

1952, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 11.4 31.6 28.7 17.7 8.3 2.1 0.1 

1953 , , . , , , . . . , , . . . , . . . . . . , , . . . . . . . . . . . 100.0 0.1 11.7 31.3 28.5 17.7 8.4 2.1 0.1 

1954 . . , . . . . , . . . . . . , , . . . . . . . . . , . , . . . . . . 100.0 0.2 11.9 31.3 28.0 18.0 8.4 2.2 0.1 

1955 . , . ! . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 12.0 31.5 27.7 17.9 8,5 2.2 0.1 

1956 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 12.5 31.9 27.2 17.5 8.5 2.2 0.1 

1957 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 12.9 32.0 26,8 17.2 8.6 2.1 0.1 

1958 . . . ! , . . , . . , . , . . . . , . . . . . . . . . . . . . . . . 100.0 0.2 13.2 32.6 26.4 16,9 8.5 2.1 0.1 

1959 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100,0 0.2 13.5 33.1 25.9 16.5 8.6 2.1 0.1 

1960 . . , . . , . . , , . . . . . . . , . . . , , . . . . , . . . . . . 100.0 0.2 13.8 33.5 25.7 16.2 8.5 2.2 0.1 

1961 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 14.1 33.9 25.3 15.9 8.3 2.2 0.1 

1962 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 14.4 34.7 25.1 15.3 8.0 2.2 0.1 

1963 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 14.3 35.5 25.0 14.9 7.9 2.2 0.1 

1964 .,...,., , . . . . . . . . , . . . . , , . . . , . . . . . . 100.0 0.2 14.5 35.7 25.0 14,5 7.7 2.2 0.1 

1965 . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 15.7 35.6 24.6 14.1 7.5 2.2 0.1 

1966 . . . . . , ! . . . . . . . . . . . . . . . . . . . . . . . . . , . 100.0 0.2 17.2 36.0 24,2 13.2 7.0 2.1 0.1 

1967 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.2 16.9 37.2 24.6 12.5 6.5 1.9 0.1 

White 

1950 . . . . ,, , , . . . . . , . . . ., , . . . , . , . . . . , . . . 100,0 0.1 10.4 31.8 29.7 17.4 8.4 2.1 0.1 

1951 . . . . . , , , . . . . . . . . . . . . , . . . . . . . . . . . , . 100.0 0.1 10.5 32.0 29.4 17.5 8.2 2.1 0.1 

1952, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 10.1 31.5 29.4 18.2 8.4 2.1 0.1 

1953 . . , . . , . . . . , , . . . . . . . . , . . . . . . . . . . . . . 100.0 0.1 10.5 31.4 29.1 18.2 8.5 2.1 0.1 

1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 10.7 31.4 28.6 18.4 8.6 2.2 0.1 

1955 . ., , . . . . . . . . . . . . . . . . . . . . . . , , . . . . . . 100.0 0.1 10.8 31.6 28.3 18.3 8.7 2.2 0.1 

1956, ,,, . ., . ., .,, . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 11.4 32.0 27.8 17.8 8.7 2.2 0.1 

1957 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 11.9 32.1 27.4 17.5 8.7 2.2 0.1 

1958 . , . . ,, . . . ., . . , , . . . , . . . , . . . . , . . . . . . 100.0 0.1 12.1 32.7 26.9 17.2 8.6 2.1 0.1 

1959, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 12.4 33.5 26.4 16.8 8.7 2.1 0.1 

1960 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 12.7 33.9 26.2 16.3 8.5 2.2 0.1 

1961 i , , , . , ,, , . , , , . . , . ., , , . . ,. . . . . . , . . . 100.0 0.1 13.1 34.3 25.6 16.1 8.4 2.2 0.1 

19621 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 13.5 35.3 25,4 15.3 8.0 2.2 0.1 

19631 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 13.3 36.2 25.4 14.9 7.8 2.2 0.1 

1964, ,, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 13.2 36.4 25.7 14.7 7.7 2.2 0.1 

1965 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100.0 0.1 14.2 36.2 25.3 14.3 7.6 2.2 0.1 

1966 . . . . . , . , , . . , . . . . , . . . . . ! . . . . . . . , . . . 100.0 0.1 15.5 36.8 25.0 13.3 7.0 2.1 0.1 

1967 . . . . . . . . . . . . . . , . . ,. . , . . , , . . . , , . . . , 100.0 0.1 14.9 38.2 25.7 12.7 6.5 1.9 0.1 

See footnote at end of table. 

45 
Table7. Percentage distribution oflive Mrthsby a~ofmother and color: United States, 1950-67-Con. 

Year and 

color 

All other 

1950 . . . . . . . . . . . . . . . . . . . . . . . . . . . ..-O.OO 

1951 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1952 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1953 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1955 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1956 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1957 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1958 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1959 . . . . . . . . . . . . . . . . . . . . . . . . .. OO..OO.. 

1960 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1961 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

19621 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

19631 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

1964 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., 

1965 . . . . . . . . . . . . . . 0. . . . , , . . , . , . . . . . . . , 

1966 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., 

1967 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

‘Figures bycolor excludecf for New Jersey. 

46 

Age of mother (veers) 

45 

Under Total 15-19 20-24 25-29 30-34 35-39 4044 and 

15 over 

100.0 0.7 20.6 32.6 23.2 13,2 7.5 2.0 0.2 

100.0 0.7 20.2 32.0 23.6 13.7 7.5 2.1 0.2 

100.0 0.6 19.5 31.6 24.3 14.4 7,4 2.1 0.2 

100.0 0.6 19.3 31.0 24.6 14.7 7.4 2.1 0.2 

100.0 0.7 19.2 31.0 24.3 15.0 7.5 2.1 0.1 

100.0 0.6 19.0 31.2 24.1 15.2 7.7 2.0 0.2 

100.0 0.7 19.1 31.3 23.7 15.3 7.8 2.0 0.1 

100.0 0.7 19.2 31.4 23.4 15.3 7.8 2.0 0.2 

100.0 0.6 19.3 31.5 23.3 15.3 7.9 2.0 0.1 

100.0 0.6 19.4 31.4 23.2 15.2 8.0 2.0 0.1 

100.0 0.6 19.6 31.5 22.9 15.1 8.o 2,1 0.1 

100.0 0.7 19.5 31.6 23.1 14.9 8.1 2.1 0.1 

100.0 0.7 19.9 32.0 22.7 14.5 7.9 2.1 0.1 

100.0 0.8 20.4 32.5 22.3 14.1 7.6 2.1 0.1 

100.0 0.8 21.5 32.6 21.7 13.7 7.5 2.2 0.1 

100.0 0.8 23,1 32,3 21.1 13.1 7.3 2.1 0.1 

100.0 0.9 25.5 32.1 20.2 12.3 6.8 2,1 0.1 

100.0 1.0 26.9 32.4 19.6 11.6 6.3 2.0 0,1 
I 

, TECHNICAL 

I 

I 

I 

DEFINITION OF LIVE BIRTH 

Every product of conception that gives signs 

of life after birth, regardless of the length of the 

pregnancy, is considered a live birth. This 

concept is embraced by the definition set forth 

by the World Health Organization as follows: 

Live birth is the complete expulsion or extraction from 

iti mother of a product of conception, irrespective of the 

duration of pregnancy, which, after such separation breathes 

m shows any other evidence of life, such as beating of the heart, 

pulsation of the umbifical cord, or definite movement of 

voluntary muscles, whether or not the umbilical cord has been 

cut or the placenta is attached; each product of such a bkth is 

considered liveborn.64 

SOURCES OF DATA 

Natality Statistics 

Natality statistics are based on information 

obtained from microfilm copies of the original 

birth certificates. These copies are received from 

the registration offices of all States, certzjn 

cities, and the District of Columbia. The statistical information on these records was edited, 

APPENDIX 

classified, placed on punchcards, and tabulated 

at the National Center for Health Statistics. In 

the statistical tabulations, United States refers to 

the aggregate of the 50 States and the District of 

Columbia. Alaska has been included in the 

United States tabulations since 1959 and Hawaii 

since 1960. . 

Natality data for the United States are limited 

to births occur.ing within the United States, 

including those occurring to nonresident aliens. 

Births occurring to U.S. citizens outside the 

United States are not included. 

Standard Certificate of Live Birth 

The Standard Certificate of Live Birth, issued 

by the Public Health Service, has served for 

many years as the principal means of attaining 

uniformity in the content of the documents 

used to collect information on births in the 

United States. It has been modified in each State 

to the extent required by the particular needs of 

the State or by special provisions of the State 

vital statistics law. However, the certificates of 

most States conform closely in content and 

arrangement to the standard certificate. 

47 
Form .p,r.”od


�ud,., SWUM M. U-MU.


mTn’IcaTE or LIVE NnTII STAIC OF mnrnm. 

JAAP OmTw 1. � ,2.:stt:~lml~ w S20’EWEWfvbb”## SOfk {Awt) 

: 6. CITY.m. 03 LccATm c. cm. Tows. 0s LOCA71014 : 

: 

i 

g c.	 SAWS or (rfncz An M**, sA?eJArwA-m) d. sTREET A~ESS 

Homru 0s 

nmVLnmR ~ 

4 B ?LAC2 * SIRtW lk31DE CITY LIMITS? c. K R331D2N22 IIWJ02 cITY LIMIT’? f. IS RE310EW23 m A FARM) 

m YESD WJO ma mu 

)** M4ue 3X 

~ 3“ %“ 

5	 4. S31 %. 7WtSDIRTH 5A IF TWIM DA TslPLEr. WAS CIIILD AOSN 6. O&TS M,AIA Lb Ytu 

WAOLE0 mm •1 TSWLETc1 1STa 201J 30 D IIW7H 

m . 

7. iLQMt F3nl MA4& w 8.- MRAC2 

~~ 

p	 “ E IO. DIRTiwk.AcE (EY@c or fortfm COMWS) t k. USUAL EICCU?AIIDA llb. KIIIO OF M331tSSS 0S INDUSTRY g c ‘“ ‘=E (At’i* Mthti ‘RA) 

z 

MWIE LAW 13. CCLOS OS RACS 

~ 

15. DIRTIWE.ACE (tlhfc w fo,titn C08@V) 16.PREVIOUS LWLNERIES TO MOTHER (& Nor hKAm& thb blrtb) 

YEARS . . M“ -, b. n“ m., OrMBe CA@- . . n“ W 

:::=IC ,~tiyl.+m im~km *i* b.f m lICA*. A-. “xx! w 

(h �n* ~i-) r 

g z Is. Mo?34srs AAAs.nk AOosEss 

~ g“ 

I’m S20wmum 1*. Al12KOAWf AT �IRTH 

:1 ~i%gg M. o. � 0,0. n Mlowm � OTHER (ihlh) 

-$ m&tk3ay I*. AOOSSS3 134 ONE *IWO 

s 19. DATE RECD. SY LOCAL REC. =. REGISTRARS SICSATUA2 21. DATfOKWHICH CIVZH SAMEAWD 

8 w (R8swm) 

k FOR A3sD2UL MAO sssabm Lms -v E 

& (2W WAS Musrkxsd Oat) 

~ a. LEKSTHC# ?ssSsAIAcY 224.WSWK ATMRIW Z. LC@lllMA7S 

3 Wn?yo Ls. cu. mD s00 I 

~ 

(4?As2mAoo4wos wW---mlmn~sTm) 

i!“ 

i # 

48 
CLASSIFICATION OF DATA 

Age of Mother 

The birth certificate asks for “age (at time of 

this birth).” 

Total-Birth Order 

Birth order shown in this report refers to the 

total number of births the mother has had, 

includlng fetal deaths. 

Race and Color 

Births in the United States are classified for 

statistical purposes according to the race of the 

parents. In this report only the classes “white” 

and “other” are used. The category “white” 

comprises births reported as white, Mexican, 

Puerto Rican, and Cuban. The category “other” 

comprises Negro, American Indian, Chinese, 

Japanes~ Hawaiian and part-Hawaiian, Aleuts 

and Eskimos and persons of any other race not 

included in “white.” 

Data by color for the years 1962 and 1963 do 

not include births in New Jersey because the 

item was omitted from the record form in those 

years. 

Place of Birth 

Births occurring in hospitals and institutions, 

regardless of the person in attendance, and those 

occurring in clinics, centers, or homes that were 

attended by physicians are included in the 

category “in hospital.” In this context the word 

“home” does not refer to the mother’s residence 

but to an institution such as a home for unwed 

mothers. 

Birth Weight 

In practically all areasbirth weight is reported 

in terms of pounds and ounces rather than in 

grams. However, the metric system has been 

used in tabulating and presenting the statistics to 

facilitate comparison with data published by 

other groups in the United States. The equivalents in pounds and ounces of the gram intervals 

are as follows: 

500 grams or less = 1 lb. 1 oz. or less 

501-1,000 grams = 1 lb. 2 oz.-2lb. 3 oz. 

1,001-1,500 grams = 2 lb. 4 oz.-3 lb. 4 oz. 

1,501-2,000 grams = 3 lb. 5 oz.-4 lb. 6 oz. 

2,001-2,500 grams = 4 lb. 7 oz.-5 lb. 8 oz. 

2,501-3,000 grams = 5 lb. 9 oz.-6 lb. 9 oz. 

3,001-3,500 grams = 6 lb. 10 oz.-7 lb. 11 oz. 

“3,501-4,000 grams = 7 lb. 12 oz.-8 lb. 13 oz. 

4,001-4,500 grams = 8 lb. 14 oz.-9 lb. 14 OZ. 

4,501-5,000 grams = 9 lb. 15 OZ.-11 lb. O OZ. 

5,001 grams or more = 11 lb. 1 oz. or more 

For purposes of classification the term “low 

birth weight” refers to infants weighing 2,500 

grams or less at birth. 

For the years 1950-55, the records for Connecticut and Massachusetts are included in the 

category “Not specified” because birth weight 

was not included on the birth record forms in 

those states. In 1956, the information became 

available for Connecticut for part of the year, 

and for the years 1957-58 only Massachusetts 

failed to include this item on its live birth record 

forms. Beginning with 1959, birth weight was 

included on the record forms of all States. 

Period of Gestation 

The period of gestation is defined as beginning with the first day of the ‘last normal 

menstrual period (LMP) and ending with the day 

of birth. The LMP is used as the initial date since 

it can be more accurately determined than the 

date of conception, which usuaIIy occurs 2 

weeks after LMP. 

The reporting of period of gestation is often 

in terms of weeks or of months of pregnancy. 

When months are reported, they are converted 

to gestation intervals in weeks as follows: 

4 months to under 20 weeks 

5 and 6 months to 20-27 weeks 

7 months to 28-31 weeks 

8 months to 32-35 weeks 

9 months to 40 weeks 

10 months to 43 weeks and over 

49 
----

Births occurring prior to 37 weeks of gestation are considered to be premature for purposes 

of classification. 

An examination of the reported information 

on period of gestation suggests a substantial 

heaping at the intervals of 36 weeks and 40 

weeks and over. These biases result from the fact 

that the gestation period is frequently not 

carefully observed and that the newborn infant 

of normal size is generally assumed to have had a 

gestation period of 40 weeks or 9 months, 

depending on conventional usage. Such errors in 

reporting are minimized in areas where the 

gestation period item on the birth certificate 

requests the “first day of the last normal 

menstrual period.” 

During the period of this study, relatively few 

areas in the United States required the entry of 

first day of the last menstrual period on their 

records. In 1958, only Baltimore, California, and 

New York City are shown as requiring this 

information in the annual volume Vital Statistics 

of the United States. By 1967, the following 

areas were added: District of Columbia beginning in 1960, Rhode Island in 1965, Minnesota 

in 1967. Inadvertently, in 1967 weeks of gestation were punched for Rhode Island instead of 

date of last normal menses as shown on the 

record form. The year which is reported here is 

not necessarily the year that the item first 

appeared on the record form, but the first year 

that data for this method of reporting are so 

identified in Vital Statistics of the United States. 

Data by gestational age are not published for 

all years, Published volumes for the years 

1954-55, 1957, 1959, and 1961 do not contain 

data by gestation. For the remaining years, the 

data do not include all of the States. For the 

following years, the exclusions are: 

1950 Louisiana, Massachusetts


1951 – – – – Massachusetts


1952-53- - – Massachusetts, Washington


1956, 1958


1960, - Maryland outside Baltimore,


1962-67 I and Massachusetts


QUALITY OF DATA 

While vital statistics data are useful for a 

variety of administrative and scientific purposes, 

they cannot be correctIy interpreted unless 

Vari-ousqualifying factors and methods of classification are taken into account. It is not feasible 

to discuss all the pertinent factors in the use of 

vital statistics tabulations, but some of the more 

important ones should be mentioned. 

Completeness of Registration 

It is estimated that 99.0 percent of all births 

occurring in the United States in 1967 were 

registered. This estimate is based on results of 

the 1950 test of birth registration completeness, 

which indicates that 98.6 percent of white births 

and 93.6 percent of nonwhite births were 

registered in that year. Estimates of birth registration completeness by color since 1933 are 

shown in the-figure. -

PERCENT COMPLETENESS OF BIRTH REGISTRATION, 

BY COLOR: UNITEO STATES, 1933.67 

(Oata for 1940 and 1950 are based on results 

of nationwide tests of registration completeness, 

Data for other yeara are estimated) 

100 m:-~l~t’’””” Iliillllllll,,,,,,,,l’, 

White 

-m---­ *4. * ** 

95 , **- #-

0’ � 

/ 

90 4 

1 / 

./ ! B5 

/ 

84 All other 

*+4 

80 F 

75 

0 II I I f 1 I I ! I I I I 1 t I r 1 1 I 1 1 I I I I I I 1 I I I I 

1933 1940 1950 1960 1970 

YEAR 

Quality Control Procedures 

The coding and punching of birth data are 

performed simultaneously directly from microfilm images or transcripts of the original certificates. Approximately 75 percent of all cards 

punched are verified on a 10-percent systematic 

I 

I 

50 
sample. The expected result from this system of 

verification is that on the average 2.25 percent 

of the cards contain one or more errors. The rest 

of the cards are verified completely, and the 

errors remaining are presumably very few. 

Sampling of Birth Records 

Birth statistics presented in this report for 

years prior to 1951 and for 1955 are based on 

the total file of birth records. Statistics for 

1951-54 and 1956-66 are based on 50-percent 

—ooo—


samples which consist of even-numbered birth 

records. During the processing of the 1967 

records, the sampling rate was reduced from 50 

percent to 20 percent. 

The sample design is essentially a stratified 

random sample. The sampling frame consists of 

births that occur in the United States during a 

calendar year and are recorded by State registrars of vital statistics. Tables of standard errors 

are included in the annual volumes Vital Statistics of the United States for the appropriate 

years. 

51

Series 1. 

Series 2. 

Series 3. 

Series 4. 

Series 10. 

VITAL AND HEALTH STATISTICS PUBLICATION SERIES 

Formerly Public Health Service Publication No. 1000 

Programs and collection procedures. — Reports which describe the general programs of the National 

Center for Health Statistic and its offices and divisions, data collection methods used, definitions, 

and other material necessary for understanding the data. 

lMta evaluation and methods vesearch.— Studies of new statistical methodology including: experimental tests of new survey methods, studies of vital statistics collection methods, new analydcal 

techniques, objective evaluations of reliabiliw of collected data, contributions to statistical theorY. 

Analytical studies .-Reports presenting analytical or interpretive studies basedon vital and health 

statistics, carrying the analysis further than the expository types of reports in the other series. 

Documents and committee veports.— Final reports of major committees concerned with vital and 

health statistics, and documents such as recommended model vital registration laws and revised 

birth and death certificates. 

Data from the Health Interview Swvvey.—Statistics on illness, accidental injuries, disability, use 

of hospital, medical, dental, and other services, and other health-related topics, based on data 

collected in a continuing national household interview survey. 

Series11. Data from the Health Examination Survey. —Data from direct examination, testing, and measureSeries 12. 

Series 13. 

Series 14. 

Se7ies 20. 

Series 21. 

Series 22. 

For a list 

ment of national samples of the civilian, noninstitutional population provide the basis for two types 

of reports: (1) estimates of the medically defined prevalence of specific diseases in the United 

States and the distributions of the population with respect to physical, physiological, and psychological characteristics; and (2) analysis of relationships among the various measurements without 

reference to an explicit finite universe of persons. 

Data from the Institutional Population Surveys. —Statistics relating to the health characteristics of 

persons in institutions, and their medical, nursing, and personal care received, based on natiomd 

samples of establishments providing these services and samples of the residents or patients. 

Data from the Hospital Discharge Survey. —Statistics relating to discharged patients in short-stay 

hospitals, based on a sample of patient records in a national sample of hospitals. 

Data on health resouvces: manpower and facilities. —Statistics on the numbers, geographic distribution, and characteristics of health resources including physicians, dentists, nurses, other health 

occupations, hospitals, nursing homes, and outpatient facilities. 

Datu on mortality. —Various statistics on mortality other than as included in regular snnwd or 

monthly reports - special analyses by cause of death, age, and otiier demographic variables, also 

geographic and time series analyses. 

Data on natality, marriage, and divovce. —Various statistics on natality, marriage, and divorce 

other than as included in regular annual or monthly reports-special analyses by demographic 

variables, also geographic and time series analyses, studies of fertility. 

Data j?om the National Natality and Mortality Surveys. — Statistics on ch~-acteristics of births 

and deaths not available from the vital records, based on sample surveys stemming from these 

records, including such topics as mortality by socioeconomic class, hospital experience in the 

last year of life, medical care during pregnancy, health insurance coverage, etc. 

of titles of reports published in these series, write to: Office of Information 

National Center for Health Statistics 

Public Health Service, HSMHA 

Rockville, h4d. 20852