Maternal Mortality and

Related Concepts

Series 3, Number 33 February 2007
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Maternal mortality and related concepts.

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Series 3, Number 33

Maternal Mortality and

Related Concepts

Analytical and Epidemiological

Studies

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Hyattsville, Maryland

February 2007

DHHS Publication No. (PHS) 2007-1417
National Center for Health Statistics

Edward J. Sondik, Ph.D., Director

Jennifer H. Madans, Ph.D., Acting Co-Deputy Director

Michael H. Sadagursky, Acting Co-Deputy Director

Jennifer H. Madans, Ph.D., Associate Director for Science

Jennifer H. Madans, Ph.D., Acting Associate Director for

Planning, Budget, and Legislation

Michael H. Sadagursky, Associate Director for

Management and Operations

Lawrence H. Cox, Ph.D., Associate Director for Research

and Methodology

Margot A. Palmer, Director for Information Technology

Margot A. Palmer, Acting Director for Information Services

Linda T. Bilheimer, Ph.D., Associate Director for Analysis

and Epidemiology

Charles J. Rothwell, M.S., Director for Vital Statistics

Jane E. Sisk, Ph.D., Director for Health Care Statistics

Jane F. Gentleman, Ph.D., Director for Health Interview

Statistics

Clifford L. Johnson, Director for Health and Nutrition

Examination Surveys

Division of Vital Statistics

Charles J. Rothwell, M.S., Director

James A. Weed, Ph.D., Deputy Director

Robert N. Anderson, Ph.D., Chief, Mortality Statistics

Branch
Contents
 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
 

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

Maternal Mortality and the NVSS, 1900–1998 ................................................................... 2 
 

Coding Practices ......................................................................................... 2 
 

Recent Changes, 1999–2003.................................................................................. 3 
 

Methods .................................................................................................. 4 
 

Results ................................................................................................... 5 
 

New Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 
 

Discussion ................................................................................................ 5 
 

References ................................................................................................ 6 
 

Appendix ................................................................................................ 11 
 

Technical Notes ......................................................................................... 11 
 

Text Figures

1. Maternal mortality rates, United States, 1915–2003......................................................... 2 
 

2. Definitions in ICD–10 ................................................................................ 3 
 

Text Tables

A. Maternal death cause-of-death codes by the International Classification of Diseases (ICD) Revision................. 2 
 

B. Maternal mortality rates by question type: United States, 1996–2003 .......................................... 5 
 

Detailed Tables

1. Maternal mortality rates by race, birth-registration states, or United States, 1915–2003 ............................ 8 
 

2. Maternal mortality rates by Hispanic origin and race for non-Hispanic population: United States, 1997–2003......... 10 
 

3. Maternal mortality rates by question type: United States, 1996–2003 ......................................... 10 
 

Appendix Tables

I. Implementation dates for the International Classification of Diseases Revisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 
 

II. Maternal death cause-of-death codes by the International Classification of Diseases (ICD) Revision ................ 11 
 

III. Separate questions related to pregnancy on state certificates in 2003 .......................................... 12 
 

iii
Objective

This report presents data on U.S.

deaths to pregnant or recently pregnant

women, summarizes long-term

processing issues, and examines recent

changes affecting the data and the

impact of the changes on the statistics

for these women.

Methods

This report presents descriptive

tabulations of information reported on

death certificates that are completed by

funeral directors, attending physicians,

medical examiners, and coroners. The

original records are filed in the state

registration offices. Statistical

information is compiled into a national

database through the Vital Statistics

Cooperative Program of the Centers for

Disease Control and Prevention’s

(CDC) National Center for Health

Statistics (NCHS). Causes of death are

processed in accordance with the

International Classification of Diseases

(ICD).

Results

Maternal mortality fluctuates from

year to year but was 12.1 deaths per

100,000 live births in 2003. The

implementation of the International

Classification of Diseases, Tenth

Revision (ICD–10) in 1999 resulted in

about a 13 percent increase in the

number of deaths identified as maternal

deaths between 1998 and 1999. The

rate increased again between 2002 and

2003 after a separate pregnancy

question became a standard item on

the U.S. Standard Certificate of Death.

The adoption of a standard separate

question on pregnancy facilitates the

identification of late maternal deaths.

Conclusion

Maternal deaths increased with the

introduction of the ICD–10 and with

changes associated with the addition of

a separate pregnancy status question

on the U.S. Standard Certificate of

Death. These changes may result in

better identification of maternal deaths.

Keywords: maternal mortality c

maternal mortality rate c vital

statistics c U.S. Standard Certificate

of Death c ICD

Maternal Mortality and

Related Concepts

by Donna L. Hoyert, Ph.D., Division of Vital Statistics

Introduction
 

In 1915, the maternal mortality rate

was 607.9 deaths per 100,000 live births

for the birth registration area. In 2003,

the maternal mortality rate was 12.1

deaths per 100,000 live births in the

United States (Figure 1 and Tables 1 and

2). Despite this tremendous overall

improvement, maternal mortality

continues to be a significant public

health issue and commands an enormous

amount of attention. One of the

consequences of this intense scrutiny is

that enhanced surveillance efforts have

been developed to actively identify

deaths of women near the time of

pregnancy. Death certificates are a

common tool for researchers interested

in this topic and serve several roles; for

example, the source of National Vital

Statistics System (NVSS) maternal

mortality data and one of the sources

used in pregnancy mortality surveillance

efforts to identify cases.

Following the rules and regulations

of the ICD (1), the NVSS has provided

maternal death counts since 1900 and

maternal mortality rates since 1915

(Tables 1 and 2 and Figure 1). It remains

a valuable source of information on

trends and is characterized by universal

coverage and consistent data collection.

However, the NVSS does not identify as

many events as active surveillance

efforts. An evaluation study for the

1995–97 period found that 35 percent

more maternal deaths are identified

through surveillance efforts than solely

by the death certificate. A number of

explanations account for the under

ascertainment including missing

information in the cause-of-death

section, use of fewer sources, and

differences in identification (2).

As alternative data sources have

been developed and research groups

have focused on this issue in greater

detail, there has been interest in

improving the information coming from

the death certificate. Some longstanding

efforts to improve vital statistics data

quality include states querying death

certificates to get additional information

for specific records (3), and the

inclusion of a separate question on

recent pregnancy history on death

certificates in a growing number of

states. More states would likely have

adopted a separate question if it had

been on the U.S. Standard Certificate.

Although a question was proposed for

the 1979 and 1989 U.S. Standard

Certificate of Death (4,5), it was not

adopted because of a perception that

information on maternal deaths should

be reported in the existing cause-ofdeath section, the space for adding

questions on the certificate was limited,

and alternative sources measuring deaths

around the time of pregnancy existed.

The 2003 U.S. Standard Certificate of

Death did include a separate question.

This report was prepared in the Division of Vital Statistics (DVS) under the general direction of Charles

J. Rothwell, Director of DVS and Robert N. Anderson, Chief, Mortality Statistics Branch (MSB). Arialdi

Minino of MSB provided content related to comparability. Registration Methods staff and staff of the

Data Acquisition and Evaluation Branch provided consultation to state vital statistics offices regarding

collection of the death certificate data on which this report is based. This report was edited by Demarius

V. Miller, Office of Information Services, Information Design and Publishing Staff; typeset by

Jacqueline M. Davis; and the graphics produced by John Jeter, both of CoCHIS/NCHM/Division of

Creative Services.

Page 1
Page 2 [ Series 3, No. 33

NOTE: Prior to 1933, data for birth-registration states only. Line breaks are shown between successive Deaths per 100,000 live births 

1,000 

100 

10 

0 

Years 

1920 1930 1940 1950 1960 1970 1980 1990 2000 

Figure 1. Maternal mortality rates, United States, 1915–2003

International Classification of Diseases revisions. 

This report summarizes processing

of maternal mortality in the NVSS and

describes some recent changes affecting

NVSS data and their impact upon

statistics on deaths of pregnant or

recently pregnant women. Specifically,

the report examines the impact of

revision of the death certificate and ICD

(6).

Maternal Mortality and

the NVSS, 1900–1998

In the NVSS, deaths of pregnant or

recently pregnant women are identified

according to the information reported on

the women’s death certificates,

particularly the causes of death reported

by physicians, medical examiners, and

coroners. From the beginning, the ICD

included maternal causes in the list of

causes of death, so deaths from these

causes could be distinguished from

those due to other causes. Maternal

deaths were deaths where the

cause-of-death codes were identified as

complications of pregnancy, childbirth,

and the puerperium in the ICD. The

relevant codes for 1900–1998 are shown

in Table A (7–12).

Explicit definitions for terms related

to mortality around the time of

pregnancy (e.g., maternal death) were

first included in the ICD in the

International Classification of Diseases,

Table A. Maternal death cause-of-death

codes by the International Classification of

Diseases (ICD) Revision

Revision ICD Codes

First ..................... 151–159

Second ................... 134–141

Third . . . . . . . . . . . . . . . . . . . . . 143–150

Fourth . . . . . . . . . . . . . . . . . . . . 140–150

Fifth ..................... 140–150

Sixth . . . . . . . . . . . . . . . . . . . . . 640–689

Seventh ................... 640–689

Eighth . . . . . . . . . . . . . . . . . . . . 630–678

Ninth . . . . . . . . . . . . . . . . . . . . . 630–676

Ninth Revision (ICD–9), implemented

with data for 1979 (13). This

introduction of definitions clarified what

should be included in the maternal

mortality measure obtained from vital

statistics; however, the maternal death

concept according to the ICD–9 was

largely consistent with what the

National Center for Health Statistics

(NCHS) and its predecessor agencies

had been using. The main difference in

the definition of maternal deaths

introduced in the ICD–9 was that the

time frame required for designation of a

maternal death was restricted to within

42 days of the end of the pregnancy,

whereas the earlier interpretation was to

include deaths occurring anytime within

1 year of the end of a pregnancy. The

maternal conditions making up maternal

deaths continued to be grouped under a

heading that referred to pregnancy,

childbirth, and the puerperium, and the

time frame of 42 days corresponded to

common usage of the term of

puerperium as the time during which

physiologic changes women experience

while pregnant revert back to normal

(14). Some contend that the 42-day

period also reflects cultural practices as

not all physiologic changes may be

completely resolved in 42 days (15).

Nevertheless, the change in time frame

was not judged to have a substantial

impact on the statistics in the United

States around 1979 because most deaths

occur within 42 days, and the decreasing

influence of changing the time period

was overwhelmed by increases resulting

from more causes being grouped within

the section of the classification dealing

with maternal causes (16).

Coding Practices

There was no specific guidance on

maternal death coding for most years

(17,18). For most of the 1900s, a

classification rule limited a maternal

death to a death within 1 year after

termination of pregnancy from any

‘‘maternal cause.’’ If no duration was

specified and the underlying cause of

death was a maternal condition, the

duration was assumed to be within 1

year and the death was coded by NCHS

as a maternal death. If duration was

stated, then deaths occurring more than

1 year after the pregnancy ended were

not considered maternal deaths

regardless of cause (19).

General changes in 1949 had some

implications for maternal deaths (16).

The adoption of the International

Classification of Diseases, Sixth

Revision (ICD–6) brought about a

change in death certificate format and

introduced rules for selecting an

underlying cause. Previously, a joint

cause manual was used to select the

cause that would be tabulated. Using the

sequential format resulted in selecting a

maternal cause 9 percent less often than

using the joint cause manual (20).

More guidelines for maternal deaths

have been provided in subsequent years

(17). The coding guidelines continued to

focus on complications of pregnancy,

and described when to code the specific
Series 3, No. 33 [ Page 3

term ‘‘pregnancy,’’ when to use a

separate question on pregnancy, and

how to code additional available codes.

The gradual changes introduced with the

International Classification of Diseases,

Seventh Revision (ICD–7) and the

International Classification of Diseases,

Adapted, Eighth Revision (ICDA–8) had

little impact on maternal mortality

statistics (16).

In 1979, the ICD–9 (11,13) had two

main changes related to maternal deaths

(i.e., definitions and additional

categories). The impact of implementing

this revision resulted in a 10 percent

increase in maternal deaths (21). This

was the result of additional causes

considered to be maternal (indirect

obstetric causes such as infective and

parasitic conditions and other current

conditions in the mother that are

classifiable elsewhere but which

complicate pregnancy such as syphilis,

tuberculosis, diabetes, drug dependence,

and congenital cardiovascular disorders).

The time period for a maternal death

was shortened from 1 year to 42 days;

however, this did not offset the impact

of including indirect causes.

Separate pregnancy questions

introduced by some states were

supplemental sources of information but

were not used in coding cause of death

according to ICD–9 if sufficient

information was written in the

cause-of-death statement. However, a

positive response to the separate

question was interpreted as if

‘‘pregnant’’ was reported in Part II of

the cause-of-death section of the death

certificate if it was not already reported

in the cause-of-death section.

In 1992 (17), guidance on the use

of separate questions was broadened

slightly. In addition to using questions

with a specific time, questions referring

to the 42-day period could also be used.

After meeting with CDC’s Division of

Reproductive Health (DRH) in 1997,

NCHS implemented the following

modifications for the remainder of the

time that the ICD–9 was to be used: a)

assume that death occurred within 42

days if no specific duration was

mentioned and the state did not have a

separate question on pregnancy status

and b) if a state had a separate question,

do not assume that death occurred

within 42 days unless this is specifically

reported.

Recent Changes,

1999–2003

Revisions in the latest ICD and the

U.S. Standard Certificate of Death both

were relevant for maternal mortality.

The ICD–10, which provides

cause-of-death titles and codes, coding

rules and procedures, and definitions,

was implemented in the United States in

1999 (1). The following describes

modifications between ICD–9 and

ICD–10 with respect to cause-of-death

titles, coding rules, and definitions. The

ICD–9 definitions for maternal deaths,

direct obstetric deaths, and indirect

obstetric deaths were retained in

ICD–10 (1,13). New definitions were

introduced for ‘‘Late maternal death’’

and ‘‘Pregnancy-related death’’

(Figure 2). This complicated a

pre-existing situation in which programs

conducting surveillance efforts such as

CDC’s DRH and the ICD (and

consequently the NVSS) used different

terms for similar concepts (e.g., DRH’s

pregnancy-related death term is similar

to ICD’s maternal deaths while DRH’s

Figure 2. Definitions in ICD–10

pregnancy-associated death is similar to

ICD’s pregnancy-related death term)

(21).

In 1999, the coding guidelines used

in the United States (17) were expanded

to cover additional categories available

in the ICD–10. Furthermore, if only

indirect maternal causes of death (i.e., a

previously existing disease or a disease

that developed during pregnancy that

was not due to direct obstetric causes

but was aggravated by physiologic

effects of pregnancy) were reported in

Part I and pregnancy was reported in

either Part I or II, the death was

classified as a maternal death. In

contrast, in the ICD–9, the pregnancy

had to be reported in Part I for the death

from indirect causes to be considered a

maternal death.

Along with the new definitions, the

ICD–10 introduced new details and

categories in the cause-of-death titles

associated with pregnancy, childbirth,

and the puerperium. For example, the

causes O96 Death from any obstetric

cause occurring more than 42 days but

less than one year after delivery and

O97 Death from sequelae of direct

obstetric causes were added for deaths

that occur beyond the maternal death

‘‘Maternal deaths’’ are defined by the World Health Organization as ‘‘the death

of a woman while pregnant or within 42 days of termination of pregnancy,

irrespective of the duration and the site of the pregnancy, from any cause

related to or aggravated by the pregnancy or its management, but not from

accidental or incidental causes.’’

‘‘Late maternal deaths’’ are defined as ‘‘the deaths of a woman from direct or

indirect obstetric causes more than 42 days but less than one year after

termination of pregnancy.’’

‘‘Pregnancy-related deaths’’ are defined as ‘‘the death of a woman while

pregnant or within 42 days of termination of pregnancy, irrespective of the

cause of death.’’

‘‘Direct obstetric deaths: those resulting from obstetric complications of the

pregnant state (pregnancy, labour and puerperium), from interventions,

omissions, incorrect treatment, or from a chain of events resulting from any of

the above.’’

‘‘Indirect obstetric deaths: those resulting from previous existing disease or

disease that developed during pregnancy and which was not due to direct

obstetric causes, but which was aggravated by physiologic effects of

pregnancy.’’
Page 4 [ Series 3, No. 33

period. Also, the ICD now recommends

that countries include separate questions

about recent pregnancies on their death

certificates.

Consequently, the 2003 revision of

the U.S. Standard Certificate of Death

(23) introduced the following standard

question format with response categories

to take advantage of additional codes in

the ICD–10 for deaths with a connection

to pregnancy, childbirth, and the

puerperium:

36. IF FEMALE:

h Not pregnant within past year

h Pregnant at time of death

h Not pregnant, but pregnant

within 42 days of death

h Not pregnant, but pregnant

43 days to 1 year before death

h Unknown if pregnant within

the past year

The detail of the question also

facilitates use of new concepts in the

ICD–10.

By 2003, 21 states had a separate

question related to the pregnancy status

of female decedents around the time of

their death and two states had a prompt

encouraging certifiers to report recent

pregnancies on the death certificate;

however, there were at least six different

questions being used. In 2003, only four

states could capture information

consistent with the standard. As states

revise their certificates, most states are

expected to introduce the standard item

or replace pre-existing questions with

the standard item, so that there will be

wider adoption of a pregnancy status

item across the country and greater

standardization of the particular item

used. See ‘‘Technical Notes’’ for a

listing of states and their separate

questions.

Changes in the coding guidelines on

how to use information reported in

separate pregnancy questions were

slightly more consequential with

modifications associated with the

implementation of the ICD–10 in 1999

than with modifications associated with

the revision of the death certificate in

2003. The guidelines have described the

use of separate questions as

supplemental information throughout

this period. Prior to 1999, if a specified

length of time was not provided by the

medical certifier, it was assumed that

the pregnancy terminated within 42 days

of death if the state did not have a

separate question. This assumption was

broadened to include states with

separate questions in 1999. In 2003, the

coding guidelines were modified to

reflect the specific wording of the

pregnancy status question on the 2003

U.S. Standard Certificate of Death.

Although information from separate

questions had been used previously, the

inclusion of a question on the U.S.

Standard Certificate of Death in 2003

raised the status of the item and resulted

in more guidelines for those with

nonstandard questions. In addition to the

general coding guidelines for the

standard questions, instructions for the

jurisdictions’ specific questions were

developed and distributed to the states

beginning in 2003. Data from the states

with nonstandard questions were used to

the extent possible. If the state question

identified any of the specific categories

in the standard question, then the

information was used in the same way

as the standard to assign codes. If the

state question collapsed categories, then

the information was treated as if the

pregnancy occurred for the later

category being collapsed. For example,

for the states that asked if a pregnancy

occurred within the year, this category is

equivalent to combining the standard

item’s categories of ‘‘pregnant at time of

death’’; ‘‘not pregnant, but pregnant

within 42 days of death’’; and ‘‘not

pregnant, but pregnant 43 days to 1 year

before death.’’ A positive response to

this nonstandard category without

further specification of timing in the

cause-of-death statement was treated as

if the pregnancy occurred between 43

days and 1 year before death.

Following the guidelines for coding,

maternal deaths are now identified using

the reported causes of death and a

separate question if the information

captured in the separate question was

not already reported in the cause-ofdeath section. If the woman was

pregnant at the time of death, the

medical conditions on the death

certificate are assigned to one of the

categories for conditions related to

pregnancy. If the woman was pregnant

within 42 days, the medical conditions

on the death certificate are assigned to

one of the categories for conditions

related to delivery. If the woman was

pregnant between 43 days and 1 year,

then the medical condition would be

assigned to the late maternal death

category. If the woman was pregnant

more than a year ago, direct maternal

medical conditions are assigned the

category for sequelae of direct obstetric

causes.

Methods

Data presented in this report are

based on information from death

certificates filed in the 50 states and the

District of Columbia that are

subsequently compiled into national

data, also known as NVSS, by NCHS.

Physicians, medical examiners, and

coroners are responsible for completing

the medical portion of the death

certificate.

This report presents the number of

maternal and late maternal deaths as

well as maternal mortality rates. These

rates were computed by dividing the

number of deaths (Figure 2) by the

number of live births registered for the

same period and are presented as rates

per 100,000 live births (1). The number

of live births used in the denominator is

an approximation of the population of

pregnant women who are at risk of a

maternal death. These have long been

defined as rates although other

researchers refer to equivalent measures

as ratios (22).

To assess the impact of having a

separate question on maternal mortality,

the states were divided according to

whether the state death certificate

included any form of a separate

pregnancy question. The number with a

separate question was 16 in 1996–1998,

17 in 1999–2000, 18 in 2001–2002, and

21 in 2003. The states were not grouped

further according to the particular

question used because of the small

number of deaths involved.

Maternal mortality is a relatively

rare event, so the rates fall within fairly

wide confidence intervals. Confidence

intervals are presented in Tables A and 3

to illustrate the degree of variation. To
Series 3, No. 33 [ Page 5

increase statistical reliability and assess

if any additional patterns emerge,

maternal mortality rates were also

calculated by combining the number of

deaths and births for the following

years: 1997–1998, 1999–2000, and

2001–2002.

Comparisons made in the text

among rates, unless otherwise specified,

are statistically significant at the .05

level of significance. Lack of comment

in the text about any two rates does not

mean that the difference was tested and

found not to be significant at this level.

See the ‘‘Technical Notes’’ for further

details on random variation and

calculations used in this report.

Results

Maternal mortality rates (Tables 1–

3) fluctuate considerably from year to

year, and the differences have rarely

been statistically significant in the last

few decades because of the small

numbers of events. The rates (see

Table II for ICD–9 and ICD–10 codes)

did increase between 1998 and 1999 and

between 2002 and 2003.

The increase between 1998 and

1999 results from the implementation of

the ICD–10. The changes to the ICD

and associated coding procedures for

maternal deaths account for a 13 percent

increase in the number of maternal

deaths between ICD–9 and ICD–10 data

(i.e., the comparability ratio is 1.1263).

This reflects that more indirect deaths

are identified as maternal deaths in

Maternal mortality rates (Tables B

and 3) were also affected by the

adoption of a separate pregnancy

question on the U.S. Standard

Certificate of Death. The maternal

mortality rate did not increase by a

statistically significant margin between

2002 and 2003 for the states without a

question, but the maternal mortality rate

was 20 percent greater in the states with

a separate question than in the areas

without a separate question in 2003.

Although the maternal mortality rate

increased between 2002 and 2003 for

the group of states that had the same

question in both years (40 percent), it

increased by a larger margin when the

states that adopted the new standard

question were also included

(53 percent). For individual years before

2003, the rates for states with a question

were not consistently or statistically

significantly greater than those for the

states without a question. When the data

were collapsed across time, there

seemed to be a tendency for the states

with a question to have higher rates than

those without a separate question;

however, the differences were still not

statistically different.

New Information

The ICD–10 provided categories for

late maternal deaths and sequelae of

maternal deaths. There are some records

with these new codes. For 1999–2002,

an additional 2 to 9 late maternal deaths

(O96 Death from any obstetric cause

occurring more than 42 days but less

than 1 year after delivery) and 6 to 13

sequelae of maternal deaths (O97 Death

from sequelae of direct obstetric causes)

were reported in the United States each

year. In 2003, the respective numbers

were 46 and 4. Some records may be

coded to these categories, particularly

late maternal deaths, instead of as

maternal deaths if the only information

on the timing of the pregnancy comes

from a nonstandard question. For

example, if the question refers to death

occurring within 12 months, the death

might have occurred within 42 days but

the question does not distinguish which

ones, so the coding procedure

conservatively treats the death as having

occurred between 43 days and 1 year.

Discussion

The NVSS is a longstanding source

of data on maternal mortality. However,

research (2,24–26) has demonstrated that

additional maternal deaths and other

deaths among recently pregnant women

can be identified with more effort. For

the states that had a separate question

on pregnancy status in the early 1990s,

a research study (24)

Table B. Maternal mortality rates by question type: United States, 1996–2003

[By state of residence. Rates are the sum of deaths for the time period divided by the sum of the live births for

the time period times 100,000. The numbers shown in parentheses are the confidence intervals for the rates]

ICD–10 because the procedures take Areas with a Areas without a

into account pregnancies reported in Year United States separate question separate question

both Parts I and II, whereas ICD–9 only 2003 .............. 12.1 13.0 10.8

considered deaths from indirect causes (11.0,13.2) (11.6,14.4) (9.2,12.4)

to be maternal deaths when the 2002 .............. 8.9 8.5 9.2

pregnancy was reported in Part I. The

assumption that pregnancies without 2001 ..............

(8.0,9.8)

9.9

(8.9,10.9)

(7.1,9.8)

10.3

(8.9,11.8)

(8.0,10.5)

9.5

(8.2,10.8)

specification of timing occur within 42 2000 .............. 9.8 9.6 9.9

days being applied for more states may (8.8,10.7) (8.2,11.1) (8.6,11.2)

also account for some additional deaths. 1999 .............. 9.9 10.7 9.2

When the rates are modified to take into 19981 .............

(8.9,10.9)

8.0

(9.2,12.3)

7.7

(7.9,10.5)

8.3

account the comparability ratio (7.1,9.0) (6.3,9.1) (7.0,9.5)

(Table B), the difference between 1998 19971 ............. 9.5 10.0 9.1

and 1999 is no longer statistically

significant.

19961 .............

(8.5,10.5)

8.5

(7.5,9.5)

(8.4,11.6)

9.2

(7.7,10.8)

(7.8,10.4)

8.0

(6.7,9.2)

1

Rates were modified with the comparability ratio of 1.1263.
Page 6 [ Series 3, No. 33

identified about 29 percent of the events

related to pregnancy within 1 year of

death solely through the information

reported on the checkbox.

In the NVSS, maternal deaths

increased with the introduction of the

ICD–10 and when the separate

pregnancy status question switched from

being supplemental information

available from some state certificates to

an item expected to be included on all

state certificates. Maternal mortality

rates increased for both of the years

when these changes affecting

identification of maternal deaths were

implemented. Changes with the ICD–10

that resulted in more indirect maternal

causes apply more with the increasing

use of separate pregnancy questions.

Because most states have yet to adopt

the standard format of the separate

pregnancy question, it is likely that

maternal and late maternal death rates in

all states will continue to be subject to

increases because of the adoption of

questions rather than actual increases in

maternal mortality. The ‘‘pregnancyrelated mortality rates’’ using

surveillance data increased between

1991 and 1999 (18). The increase in the

surveillance data was attributed in large

part to improved identification of

‘‘pregnancy-related deaths’’ (18).

Having supplemental information

provided by a separate question

potentially results in more death

certificates having information on them

that can be used in assigning codes in

the section of the classification

dedicated to complications of pregnancy,

childbirth, and the puerperium. The new

guidance in the special rules may have

been easier for the states with

nonstandard questions to follow because

the instructions were tailored to the

specific question on each state’s

certificate. However, the standard

question seemed to result in more

maternal deaths being identified than

other questions do. In part, this reflects

that if the timing of the pregnancy is not

stated in the cause-of-death statement

and an area has nonstandard categories

for their separate questions such as

pregnant within 12 months, then the

medical coders treat this as a death

occurring between 43 days and 1 year.

As more states adopt separate pregnancy

questions consistent with the standard,

the overall maternal mortality rate will

likely continue to drift upward because

the standard question captures more

information.

The increasing use of a pregnancy

status checkbox on death certificates and

changes in the coding under the

ICD–10, particularly of indirect maternal

causes, results in the identification of

more maternal deaths in the NVSS.

Conceivably, the differential between the

NVSS and surveillance efforts will

decrease as a result. Recent maternal

mortality rates appear to be more similar

to the ‘‘pregnancy-related mortality

rates’’ published using surveillance data

through 1999 (18), and the ratio of

deaths of recently (i.e., within 42 days)

pregnant women from causes unrelated

to pregnancy to those from maternal

causes in the NVSS is generally similar

to that found in a 1993–1998 Maryland

study using enhanced surveillance (26).

However, the distribution of the timing

of deaths suggests differences between

NVSS data and Maryland’s enhanced

data (26). Furthermore, the newer NVSS

procedures are more inclusive of

indirect causes than the surveillance

efforts (18). Future studies such as

MacKay, et al. (2) will be needed to

examine the current differential between

the NVSS data and pregnancy

surveillance efforts. Finally, surveillance

efforts should be able to take advantage

of this new question to improve the

usefulness of the death certificate as one

of the sources to identify deaths of

interest.

References

1.World Health Organization.

International Statistical Classification of

Diseases and Related Health Problems,

Tenth Revision. Geneva: World Health

Organization. 1992.

2.MacKay AP, Berg CJ, Duran C, Chang

J, Rosenberg H. An assessment of

pregnancy-related mortality in the

United States. Paediatr Perinat

Epidemiol 19(3): 206–14. 2005.

3.National Center for Health Statistics.

Vital statistics, ICD–10 cause-of-death

querying, 2006. NCHS instruction

manual; part 20. Hyattsville, MD:

Public Health Service. 2006. Available

from: http://www.cdc.gov/nchs/data/dvs/

Instruction%20Manual%2020_

%202006%20edition_w.pdf.

4.Dundon JL, Gay GA, George JL. The

1978 revision of the U.S. standard

certificates. National Center for Health

Statistics. Vital Health Stat 4(23). 1983.

Available from: http://www.cdc.gov/

nchs/data/series/sr_04/sr04_023.pdf.

5.Tolson GC, Barnes JM, Gay GA,

Kowaleski JL. The 1989 revision of the

U.S. standard certificates and reports.

National Center for Health Statistics.

Vital Health Stat 4(28). 1991. Available

from: http://www.cdc.gov/nchs/data/

series/sr_04/sr04_028.pdf.

6.National Center for Health Statistics.

Report of the Panel to Evaluate the

U.S. Standard Certificates. National

Center for Health Statistics. 2000.

Available from: http://www.cdc.gov/

nchs/data/dvs/panelreport_ acc.pdf.

7.Hetzel AM. History and organization of

the vital statistics system. National

Center for Health Statistics. 1997.

8.U.S. Census Bureau. Mortality

Statistics 1900–1904. Special reports of

the Census Office. Washington:

Government Printing Office. 1906.

Available from: http://www.cdc.gov/

nchs/data/vsushistorical/

mortstatsh_1900-1904.pdf.

9.National Office of Vital Statistics.

Maternal Mortality: United States and

each state, and Alaska, Hawaii, Puerto

Rico, and the Virgin Islands (U.S.),

1955. Vital Statistics—Special Reports:

National Summaries; vol 46 no 17.

1957.

10.National Office of Vital Statistics. Vital

statistics of the United States, 1958.

Volume I. Washington: Government

Printing Office. 1960. Available from:

http://www.cdc.gov/nchs/data/vsus/

VSUS_1958_1.pdf.

11.National Center for Health Statistics.

Vital statistics of the United States,

1968, vol II part A, mortality.

Rockville, MD: Public Health Service.

1972. Available from: http://

www.cdc.gov/nchs/data/vsus/

mort68_2a.pdf.

12.National Center for Health Statistics.

Vital statistics of the United States,

1979, vol II part A, mortality.

Washington: Public Health Service.

1984. Available from: http://

www.cdc.gov/nchs/data/vsus/

mort79_2a.pdf.

13.World Health Organization. Manual of

the International Statistical

Classification of Diseases, Injuries, and

Causes of Death, based on the
Series 3, No. 33 [ Page 7

recommendations of the Ninth Revision

Conference, 1975. Geneva: World

Health Organization. 1977.

14.	 Cunningham FG, Williams JW.

Williams Obstetrics. 21st ed. New

York, New York: McGraw-Hill. 2001.

15.	 Hoj L, da Silva D, Hedegaard K,

Sandstrom A, Aaby P. Maternal

mortality: only 42 days? BJOG: An

International Journal of Obstetrics and

Gynaecology 110(11): 995–1000. 2003.

16.	 National Center for Health Statistics.

Vital statistics of the United States,

1980, vol II part A, mortality.

Washington: Public Health Service.

1985. Available from: http://

www.cdc.gov/nchs/data/vsus/

mort80_2a.pdf.

17.	 National Center for Health Statistics.

Vital statistics, instructions for

classifying multiple causes of death.

NCHS instruction manual; part 2b.

Hyattsville, MD: Public Health Service.

Published annually.

18.	 Chang J, Elam-Evans LD, Berg CJ,

Herndon J, Flowers L, Seed KA,

Syverson CJ. Pregnancy-Related

Mortality Surveillance—United States,

1991–1999. MMWR Surveillance

Summaries 52(SS-2): 1–8. 2003.

19.	 Hoyert DL, Arias E, Smith BL,

Murphy SL, Kochanek KD. Deaths:

Final data for 1999. National vital

statistics reports; vol 49 no 8.

Hyattsville, MD: National Center for

Health Statistics. 2001. Available from:

http://www.cdc.gov/nchs/data/nvsr/

nvsr49/nvsr49_08.pdf.

20.	 National Office of Vital Statistics. Vital

statistics of the United States, 1950, vol

I. Washington: Public Health Service.

1954. Available from: http://

www.cdc.gov/nchs/data/vsus/

vsus_1950_1.pdf.

21.	 Klebba AJ, Scott JH. Estimates of

selected comparability ratios based on

dual coding of 1976 death certificates

by the Eighth and Ninth Revisions of

the International Classification of

Diseases. Monthly vital statistics report;

vol 28 no 11, supp. Hyattsville, MD:

Public Health Service. 1980. Available

from: http://www.cdc.gov/nchs/data/

mvsr/supp/mv28_11s.pdf.

22.	 Wilcox LS, Marks JS (eds). From data

to action, CDC’s Public Health

Surveillance for women, infants, and

children. U.S. Dept of Health and

Human Services, CDC Monograph.

1995.

23.	 National Center for Health Statistics.

2003 revision of the U.S. Standard

Certificate of Death. 2003. Available

from: http://www.cdc.gov/nchs/data/dvs/

DEATH11-03final-acc.pdf.

24.	 MacKay AP, Rochat R, Smith JC, Berg

CJ. The check box: Determining

pregnancy status to improve maternal

mortality surveillance. Am J Prev Med

19(1S): 35–9. 2000.

25.	 Baker N, Fogarty C, Stroud D, Rochat

R. Enhanced pregnancy-associated

mortality surveillance: Minnesota,

1990–1999. Minnesota Medicine 87(1):

45–7. 2004.

26.	 Horon IL, Cheng D. Enhanced

surveillance for pregnancy-associated

mortality—Maryland, 1993–1998.

JAMA 285(11): 1455–9. 2001.

27.	 National Center for Health Statistics.

Technical appendix. Vital statistics of

the United States, vol II part A,

mortality. Washington: Public Health

Service. Published annually. Available

from: http://www.cdc.gov/nchs/datawh/

statab/pubd/ta.htm.

28.	 Chiang CL. Introduction to stochastic

processes in biostatistics. New York:

Wiley. 1968.

29.	 Brillinger DR. The natural variability of

vital rates and associated statistics.

Biometrics 42: 693–734. 1986.

30.	 Hoyert DL, Heron M, Murphy SL,

Kung HC. Deaths: Final data for 2003.

National vital statistics reports; vol 54

no 13. Hyattsville, MD: National

Center for Health Statistics. 2006.

31.	 Schenker N, Gentleman JF. On judging

the significance of differences by

examining the overlap between

confidence intervals. The American

Statistician 55: 182–6. 2001.
Page 8 [ Series 3, No. 33

Table 1. Maternal mortality rates by race, birth-registration states, or United States, 1915–2003

[Beginning in 1989, race for live births is tabulated according to race of mother. Data are for a registration area for 1915–1932 and for the United States since 1933.

Beginning 1970 excludes deaths of nonresidents of the United States. Rates per 100,000 live births in specified group. Deaths are classified according to the International

Classification of Diseases in use at the time]

All

Year races1 White Black

Race of mother2

2003 ..................... 12.1 8.7 30.5

2002 ..................... 8.9 6.0 24.9

2001 ..................... 9.9 7.2 24.7

2000 ..................... 9.8 7.5 22.0

1999 ..................... 9.9 6.8 25.4

1998 ..................... 7.1 5.1 17.1

1997 ..................... 8.4 5.8 20.8

1996 ..................... 7.6 5.1 20.3

1995 ..................... 7.1 4.2 22.1

1994 ..................... 8.3 6.2 18.5

1993 ..................... 7.5 4.8 20.5

1992 ..................... 7.8 5.0 20.8

1991 ..................... 7.9 5.8 18.3

1990 ..................... 8.2 5.4 22.4

1989 ..................... 7.9 5.6 18.4

Race of child3

1993 ..................... 7.5 4.9 19.1

1992 ..................... 7.8 5.1 19.5

1991 ..................... 7.9 5.9 17.2

1990 ..................... 8.2 5.5 21.1

1989 ..................... 7.9 5.7 17.5

1988 ..................... 8.4 5.9 19.5

1987 ..................... 6.6 5.1 14.2

1986 ..................... 7.2 4.9 18.8

1985 ..................... 7.8 5.2 20.4

1984 ..................... 7.8 5.4 19.7

1983 ..................... 8.0 5.9 18.3

1982 ..................... 7.9 5.8 18.2

1981 ..................... 8.5 6.3 20.4

1980 ..................... 9.2 6.7 21.5

1979 ..................... 9.6 6.4 25.1

1978 ..................... 9.6 6.4 25.0

1977 ..................... 11.2 7.7 29.2

1976 ..................... 12.3 9.0 29.5

1975 ..................... 12.8 9.1 31.3

1974 ..................... 14.6 10.0 38.3

1973 ..................... 15.2 10.7 38.4

19724 .................... 18.8 14.3 40.7

1971 ..................... 18.8 13.0 48.3

1970 ..................... 21.5 14.4 59.8

1969 ..................... 22.2 15.5 59.5

1968 ..................... 24.5 16.6 65.9

1967 ..................... 28.0 19.5 72.6

1966 ..................... 29.1 20.2 74.2

1965 ..................... 31.6 21.0 88.3

1964 ..................... 33.3 22.3 93.8

19635 .................... 35.8 24.0 101.1

19625 .................... 35.2 23.8 99.4

1961 ..................... 36.9 24.9 105.4

1960 ..................... 37.1 26.0 103.6

1959 ..................... 37.4 25.8 105.0

1958 ..................... 37.6 26.3 104.5

1957 ..................... 41.0 27.5 121.6

1956 ..................... 40.9 28.7 114.3

1955 ..................... 47.0 32.8 134.3

1954 ..................... 52.4 37.2 145.9

1953 ..................... 61.1 44.1 168.3

1952 ..................... 67.8 48.9 189.2

1951 ..................... 75.0 54.9 204.2

See footnotes at end of table.
Series 3, No. 33 [ Page 9

Table 1. Maternal mortality rates by race, birth-registration states, or United States, 1915–2003—Con.

[Beginning in 1989, race for live births is tabulated according to race of mother. Data are for a registration area for 1915–1932 and for the United States since 1933.

Beginning 1970 excludes deaths of nonresidents of the United States. Rates per 100,000 live births in specified group. Deaths are classified according to the International

Classification of Diseases in use at the time]

All

Year races1 White Black

Race of child3

—Con.

1950 ..................... 83.3 61.1 223.0

1949 ..................... 90.3 68.1 237.6

1948 ..................... 116.6 89.4 303.6

1947 ..................... 134.5 108.6 336.2

1946 ..................... 156.7 130.7 363.6

1945 ..................... 207.2 172.1 456.7

1944 ..................... 227.9 189.4 513.9

1943 ..................... 245.2 210.5 512.8

1942 ..................... 258.7 221.8 549.1

1941 ..................... 316.5 266.0 690.2

1940 ..................... 376.0 319.8 781.7

1939 ..................... 403.9 352.8 771.3

1938 ..................... 435.2 377.2 861.0

1937 ..................... 488.8 436.1 862.2

1936 ..................... 568.0 511.6 980.9

1935 ..................... 582.1 530.6 954.8

19346,7

.................... 593.2 544 - - ­

19336,7 ................... 619.1 564 - - ­

19326,7 ................... 632.6 581 - - ­

19317 .................... 660.9 601 - - ­

19307 .................... 673.2 609 - - ­

19297 .................... 695.1 631 - - ­

19287 .................... 692.3 627 - - ­

19277 .................... 647.2 594 - - ­

19267 .................... 655.6 619 - - ­

19257 .................... 647.1 603 - - ­

19247 .................... 656.4 607 - - ­

19237 .................... 665.1 626 - - ­

19227 .................... 664.4 628 - - ­

19217 .................... 681.8 644 - - ­

19207 .................... 799.1 760 - - ­

19197 .................... 737.3 696 - - ­

19187 .................... 916.4 889 - - ­

19177 .................... 661.7 632 - - ­

19167 .................... 621.6 608 - - ­

19157 .................... 607.9 601 - - ­

- - - Data not available.

1

Includes races other than white and black.

2

Maternal deaths based on race of decedent; live births based on race of mother.

3

Maternal deaths based on race of decedent; live births based on race of child.

4

Deaths based on a 50 percent sample.

5

Figures by race exclude data for residents of New Jersey.

6

For 1932–1934, Mexicans are included with All other.

7

For 1915–1934, the rate for white decedents was from published figures.
Page 10 [ Series 3, No. 33

Table 2. Maternal mortality rates by Hispanic origin and race for non-Hispanic population: United States, 1997–2003

[Race for live births is tabulated according to race of mother. Excludes deaths of nonresidents of the United States. Rates per 100,000 live births in specified group. Deaths

are classified according to the International Classification of Diseases in use at the time]

All Non-Hispanic Non-Hispanic

Year origins1 Hispanic Non-Hispanic2 white black

Race of mother3

2003 ..................... 12.1 10.1 12.7 8.1 31.2

2002 ..................... 8.9 7.1 9.3 5.6 24.9

2001 ..................... 9.9 9.5 10.1 6.5 24.7

2000 ..................... 9.8 9.9 9.8 6.8 22.3

1999 ..................... 9.9 8.8 10.2 6.4 25.5

1998 ..................... 7.1 5.7 7.5 4.9 17.4

1997 ..................... 8.4 8.0 8.8 5.2 21.5

1

All origins includes origin not stated.

2

Includes races other than white and black.

3

Maternal deaths based on race of decedent; live births based on race of mother.

Table 3. Maternal mortality rates by question type: United States, 1996–2003

[By state of residence. Rates are the sum of deaths for the time period divided by the sum of the live births for the time period times 100,000. The numbers shown in

parentheses are the confidence intervals for the rates]

Areas with a Areas without

Year United States separate question a separate question

2003 ..................... 12.1 13.0 10.8

(11.0,13.2) (11.6,14.4) (9.2,12.4)

2002 ..................... 8.9 8.5 9.2

(8.0,9.8) (7.1,9.8) (8.0,10.5)

2001 ..................... 9.9 10.3 9.5

(8.9,10.9) (8.9,11.8) (8.2,10.8)

2000 ..................... 9.8 9.6 9.9

(8.8,10.7) (8.2,11.1) (8.6,11.2)

1999 ..................... 9.9 10.7 9.2

(8.9,10.9) (9.2,12.3) (7.9,10.5)

1998 ..................... 7.1 6.9 7.3

(6.3,8.0) (5.6,8.1) (6.2,8.5)

1997 ..................... 8.4 8.9 8.1

(7.5,9.3) (7.4,10.3) (6.9,9.3)

1996 ..................... 7.6 8.2 7.1

(6.7,8.4) (6.8,9.6) (6.0,8.2)
Series 3, No. 33 [ Page 11

Table Therefore, considerable caution must be Appendix II. Maternal death cause-of-death

codes by the International Classification of observed in interpreting statistics based

Diseases (ICD) Revision on small numbers of deaths.

Technical Notes

Sources of Data

The National Vital Statistics System

(18,27) data shown in this report are

based on information from death

certificates filed in the 50 states and the

District of Columbia. The number of

states participating increased from 10

and the District of Columbia in 1900 to

47 and the District of Columbia in

1932. All states have provided these

data since 1933.

These mortality statistics were

compiled in accordance with World

Health Organization (WHO) regulations,

which specify that member nations

classify and code causes of death in

accordance with the current revision of

the International Classification of

Diseases (ICD). To date, 10 revisions

have been used successively in the

United States (Table I).

Maternal Mortality

Maternal deaths were defined as

those encompassing cause-of-death

codes (see Table II) associated with

complications of pregnancy, childbirth,

and the puerperium (7–12). These

cause-of-death codes reflect information

reported in the cause-of-death section of

the death certificates. Explicit definitions

for terms related to mortality around the

time of pregnancy were introduced in

the ICD-9 and expanded in the ICD-10.

Table I. Implementation dates for the

International Classification of Diseases

Revisions

Years

Revision covered

First. . . . . . . . . . . . . . . . . 1900–09

Second............... 1910–20

Third . . . . . . . . . . . . . . . . 1921–29

Fourth . . . . . . . . . . . . . . . 1930–38

Fifth. . . . . . . . . . . . . . . . . 1939–48

Sixth . . . . . . . . . . . . . . . . 1949–57

Seventh .............. 1958–67

Eighth ............... 1968–78

Ninth . . . . . . . . . . . . . . . . 1979–98

Tenth . . . . . . . . . . . . . . . . 1999–present

Revision ICD Codes

First. . . . . . . . . . . . . . . . . 151–159

Second............... 134–141

Third . . . . . . . . . . . . . . . . 143–150

Fourth ............... 140–150

Fifth. . . . . . . . . . . . . . . . . 140–150

Sixth . . . . . . . . . . . . . . . . 640–689

Seventh .............. 640–689

Eighth ............... 630–678

Ninth . . . . . . . . . . . . . . . . 630–676

Tenth . . . . . . . . . . . . . . . . A34, O00–O95,

and O98–O99

Separate Questions

In 2003, Idaho, Maryland, Montana,

New York City, and New York state had

separate questions that could provide the

detail captured in the question in the

2003 version of the U.S. Standard

Certificate (Table III). Alabama,

California, Florida, Illinois, Indiana,

Iowa, Kentucky, Louisiana, Minnesota,

Mississippi, Missouri, Nebraska, New

Jersey, New Mexico, North Dakota,

Texas, and Virginia had separate

questions; however, they were not

consistent with the detail requested in

the 2003 U.S. Standard Certificate

question. Some states send forward data

that differs from what their questions

support. For example, California is

submitting data for pregnant at the time

of death as well as the 43 days to one

year category to which deaths within a

year are assigned.

Generally, the draft-revised state

certificates that have been submitted to

NCHS for review have included the

standard question. This indicates that in

the future, the questions used across

states will be more consistent.

Random Variation

Mortality data are not subject to

sampling error, but may be affected by

random variation. That is, the number of

deaths that actually occurred may be

considered as one of a large series of

possible results that could have arisen

under the same circumstances (28,29).

When the number of deaths is small

(perhaps less than 100), random

variation tends to be relatively large.

Using the properties of the Poisson

distribution, the standard error (SE)

associated with the number of deaths

(D) is

1. SE(D) = √var(D) = √D

where var(D) denotes the variance of D.

For maternal mortality rates based

on live births (B) in the denominator,

calculation of the SE assumes random

variability in both the numerator and

denominator. The SE for the maternal

mortality rate (MMR) is

2. SE(MMR) = Œvar(D) + MMR c var(B)

= E(B)

2

Œ D2

B

D

2 + B3

where the number of births, B, is also

assumed to be distributed according to a

Poisson distribution and E(B) is the

expectation of B.

The relative standard error (RSE)

for the MMR is

SE(MMR) 1

3. RSE(MMR) = 100 = 100Œ1 + MMR D B

Suppression of unreliable rates—An

asterisk (*) is shown in place of a

mortality rate based on fewer than 20

deaths, the equivalent of an RSE of

23 percent or more. The limit of 20

deaths is a convenient, if somewhat

arbitrary, benchmark, below which rates

are considered to be too statistically

unreliable for presentation.

Confidence intervals and statistical

tests based on 100 deaths or more—

When the number of deaths is large, a

normal approximation may be used in

the calculation of confidence intervals

and statistical tests. In general, for

maternal mortality rates, the normal

approximation performs quite well when

the number of deaths is 100 or greater.

Formula 4 is used to calculate

95 percent confidence limits for the

mortality rate when the normal

approximation is appropriate.

4. Lower = MMR – 1.96(SE(MMR)) and

Upper = MMR + 1.96(SE(MMR))
Page 12 [ Series 3, No. 33

Table III. Separate questions related to pregnancy on state certificates in 2003

Alabama................... Was there a pregnancy in last 42 days? (Specify Yes, No, or Unknown)
 

California .................. If female, pregnant in last year? h Yes h No h Unknown
 

Florida . . . . . . . . . . . . . . . . . . . . If female, was there a pregnancy in the past 3 months? Yes No
 

If female aged 10–54:

h not pregnant within past year h pregnant at time of death h not pregnant, but pregnant within

Idaho..................... 42 days of death h not pregnant, but pregnant 43 days to 1 year before death h unknown if pregnant within the past year

Illinois .................... If female, was there a pregnancy in past three months? h Yes h No

Indiana. . . . . . . . . . . . . . . . . . . . Was decedent pregnant or 90 days postpartum? (Yes or no)

Iowa ..................... If female, was there a pregnancy in the past 12 months? (Specify yes or no)

Kentucky .................. If female, was there a pregnancy in the past 12 months? h Yes h No

Louisiana .................. 	 If deceased was female 10–49, was she pregnant in the last 90 days? h Yes h No h Unknown

If female:

Was decedent pregnant in the past 12 months? h Yes h No h Unknown

Maryland .................. 	 Separate fields on dates of death and delivery support capability to compute the other categories in the standard.

Was female pregnant:

At death? yes no unknown

Minnesota.................. In last 12 months? yes no unknown

Mississippi ................. Had decedent been pregnant within 90 days prior to death? h Yes h No

Missouri ................... If deceased was female 10–49, was she pregnant in the last 90 days? h Yes h No h Unknown

If female:

h not pregnant within past year h not pregnant but pregnant with 42 days of death

h not pregnant but pregnant 43 days to 1 year before death h pregnant at time of death

Montana. . . . . . . . . . . . . . . . . . . h unknown if pregnant within past year
 

Nebraska .................. If female, was there a pregnancy in the past 3 months? h Yes h No
 

New Jersey ................. If female, was she pregnant at death, or any time 90 days prior to death? h Yes h No
 

New Mexico ................ Was decedent pregnant within last 6 weeks? h Yes h No
 

If female:

h not pregnant within 1 year of death h pregnant at time of death h not pregnant at death, but pregnant within 42 days of death

h not pregnant at death, but pregnant 43 days to 1 year before death h unknown if pregnant within 1 year of death

New York City ............... 	 Also have date of outcome, so could compute intervals if needed.

If female:

h not pregnant within last year h pregnant at time of death h not pregnant, but pregnant within 42 days of death

h not pregnant, but pregnant 43 days to 1 year before death h unknown if pregnant within past year

New York State .............. Also have date of delivery, so could compute intervals if needed.

North Dakota ................ Was deceased pregnant within 18 months of death? h Yes h No

Texas .................... Was decedent pregnant at time of death h Yes h No h Unknown

within last 12 months h Yes h No h Unknown

Virginia ................... If female, was there a pregnancy in past 3 months? h Yes h No h Unknown

The resulting 95 percent confidence

interval can be interpreted to mean that

the chances are 95 out of 100 that the

‘‘true’’ mortality rate falls between the

lower and upper limits. For example,

suppose that the mortality rate is 3.9 per

100,000 live births based on 112 deaths

and 28,560 births. Lower and upper

95 percent confidence limits using

formula 4 are calculated as

Lower = 3.9 – 1.96(.37) = 3.2 and

Upper = 3.9 + 1.96(.37) = 4.6

Thus, the chances are 95 in 100 that

the true mortality rate is between 3.2

and 4.6.

When testing the difference between

two rates, MMR1 and MMR2 (each

based on 100 or more deaths), the

normal approximation may be used to

calculate a test statistic, z, such that

MMR1 – MMR2 5.	 z =

√SE(MMR1)

2 + SE(MMR2 )2

If ?z? ≥ 1.96 then the difference

between the rates is statistically

significant at the 0.05 level. If ?z? < 1.96

then the difference is not statistically

significant. Suppose that the mortality

rate is 9.9 per 100,000 live births in

2002 (MMR1) and 8.9 per 100,000 live

births in 2003 (MMR2). The SE for

each of these figures, SE(MMR1) and

SE(MMR2), is calculated using formula

2. Using formula 5, one can test if the

decrease in the rate is statistically

significant.

9.9 – 8.9 z = = 1.46
 √(0.246)2 + (0.222)2
 

Because z = 1.46 < 1.96, the

increase from 2002 to 2003 in the

mortality rate is not statistically

significant.

Confidence intervals and statistical

tests based on fewer than 100

deaths—When the number of deaths is

not large

(fewer than 100), the Poisson

distribution cannot be approximated by

the normal distribution. A method based

on the more general family of gamma

distributions, of which the Poisson is a

member, can be used to approximate

confidence intervals for deaths and

mortality rates when the number of

deaths is small (30).

The 95 percent confidence limits

can be estimated using the lower and

upper confidence limit factors shown in

the ‘‘Technical Notes’’ of ‘‘Deaths: Final

Data for 2003’’ (30) or obtained using

the function ‘‘gammainv(probability,

alpha,beta)’’ in Excel. For the mortality

rate, MMR, the lower and upper

confidence limit factors that correspond

to the adjusted number of maternal

6.	 Lower = L(1 – α,Dadj) c MMR and
 

Upper = U(1 – α,Dadj) c MMR
 

deaths, Dadj, are calculated using

formula 6. The adjusted number of
Series 3, No. 33

[ Page 13

maternal deaths take into account the

RSE of the number of maternal deaths

and live births. D c B
 Dadj =
 D+B

For example, suppose that the

mortality rate for American Indian or

Alaska Native (AIAN) persons is 5.9

per 100,000 and based on 58 deaths and

9,801 births.

58c 9,801

Dadj= = 58 
 58 + 9,801

Applying formula 7, values forL

andU for 58 deaths are multiplied by

the mortality rate, 5.9, such that

Lower= 0.75934c 5.9= 4.5 and
 

Upper= 1.29273c 5.9= 7.6
 

These confidence limits indicate

that the chances are 95 out of 100 that

the actual mortality rate for AIAN

persons is between 4.5 and 7.6 per

100,000.

When comparing the difference

between two rates, MMR

1 and MMR2

where one or both of the rates are based

on fewer than 100 deaths,a comparison

of 95 percent confidence intervals may

be used asa statistical test. If the

95 percent confidence intervals do not

overlap, then the difference can be said

to be statistically significant at the 0.05

level.A simple rule of thumb is: if

MMR

1 is greater than MMR2 then test

ifL(MMR

1

) is greater thanU(MMR

2

)

or if MMR

2 is greater than MMR1 then

test ifL(MMR

2

) is greater than

U(MMR

1). Positive tests denote

statistical significance at the 0.05 level.

Users of the method of comparing

confidence intervals should be aware

that this method isa conservative test

for statistical significance. That is, the

difference between two rates may, in

fact, be statistically significant even

though confidence intervals for the two

rates overlap (31). Thus, caution should

be observed when interpretinga

nonsignificant difference between two

rates, especially when the lower and

upper limits being compared overlap

only slightly.
Vital and Health Statistics

series descriptions

SERIES 1.	 Programs and Collection Procedures—These reports

describe the data collection programs of the National Center

for Health Statistics. They include descriptions of the methods

used to collect and process the data, definitions, and other

material necessary for understanding the data.

SERIES 2.	 Data Evaluation and Methods Research—These reports

are studies of new statistical methods and include analytical

techniques, objective evaluations of reliability of collected

data, and contributions to statistical theory. These studies

also include experimental tests of new survey methods and

comparisons of U.S. methodology with those of other

countries.

SERIES 3.	 Analytical and Epidemiological Studies—These reports

present analytical or interpretive studies based on vital and

health statistics. These reports carry the analyses further than

the expository types of reports in the other series.

SERIES 4.	 Documents and Committee Reports—These are 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.

SERIES 5.	 International Vital and Health Statistics Reports—These

reports are analytical or descriptive reports that compare U.S.

vital and health statistics with those of other countries or

present other international data of relevance to the health

statistics system of the United States.

SERIES 6.	 Cognition and Survey Measurement—These reports are

from the National Laboratory for Collaborative Research in

Cognition and Survey Measurement. They use methods of

cognitive science to design, evaluate, and test survey

instruments.

SERIES 10.	 Data From the National Health Interview Survey—These

reports contain statistics on illness; unintentional injuries;

disability; use of hospital, medical, and other health services;

and a wide range of special current health topics covering

many aspects of health behaviors, health status, and health

care utilization. They are based on data collected in a

continuing national household interview survey.

SERIES 11.	 Data From the National Health Examination Survey, the

National Health and Nutrition Examination Surveys, and

the Hispanic Health and Nutrition Examination Survey—

Data from direct examination, testing, and measurement on

representative samples of the civilian noninstitutionalized

population provide the basis for (1) medically defined total

prevalence of specific diseases or conditions in the United

States and the distributions of the population with respect to

physical, physiological, and psychological characteristics, and

(2) analyses of trends and relationships among various

measurements and between survey periods.

SERIES 12.	 Data From the Institutionalized Population Surveys—

Discontinued in 1975. Reports from these surveys are

included in Series 13.

SERIES 13.	 Data From the National Health Care Survey—These

reports contain statistics on health resources and the public’s

use of health care resources including ambulatory, hospital,

and long-term care services based on data collected directly

from health care providers and provider records.

SERIES 14.	 Data on Health Resources: Manpower and Facilities—

Discontinued in 1990. Reports on the numbers, geographic

distribution, and characteristics of health resources are now

included in Series 13.

SERIES 15.	 Data From Special Surveys—These reports contain

statistics on health and health-related topics collected in

special surveys that are not part of the continuing data

systems of the National Center for Health Statistics.

SERIES 16.	 Compilations of Advance Data From Vital and Health

Statistics—Advance Data Reports provide early release of

information from the National Center for Health Statistics’

health and demographic surveys. They are compiled in the

order in which they are published. Some of these releases

may be followed by detailed reports in Series 10–13.

SERIES 20.	 Data on Mortality—These reports contain statistics on

mortality that are not included in regular, annual, or monthly

reports. Special analyses by cause of death, age, other

demographic variables, and geographic and trend analyses

are included.

SERIES 21.	 Data on Natality, Marriage, and Divorce—These reports

contain statistics on natality, marriage, and divorce that are

not included in regular, annual, or monthly reports. Special

analyses by health and demographic variables and

geographic and trend analyses are included.

SERIES 22.	 Data From the National Mortality and Natality Surveys—

Discontinued in 1975. Reports from these sample surveys,

based on vital records, are now published in Series 20 or 21.

SERIES 23.	 Data From the National Survey of Family Growth—These

reports contain statistics on factors that affect birth rates,

including contraception, infertility, cohabitation, marriage,

divorce, and remarriage; adoption; use of medical care for

family planning and infertility; and related maternal and infant

health topics. These statistics are based on national surveys

of women of childbearing age.

SERIES 24.	 Compilations of Data on Natality, Mortality, Marriage, and

Divorce—These include advance reports of births, deaths,

marriages, and divorces based on final data from the National

Vital Statistics System that were published as National Vital

Statistics Reports (NVSR), formerly Monthly Vital Statistics

Report. These reports provide highlights and summaries of

detailed data subsequently published in Vital Statistics of the

United States. Other special reports published here provide

selected findings based on final data from the National Vital

Statistics System and may be followed by detailed reports in

Series 20 or 21.

For answers to questions about this report or for a list of reports published

in these series, contact:

Information Dissemination Staff

National Center for Health Statistics

Centers for Disease Control and Prevention

3311 Toledo Road, Room 5412

Hyattsville, MD 20782

1-866-441-6247
 

E-mail: nchsquery@cdc.gov
 

Internet: www.cdc.gov/nchs
 
U.S. DEPARTMENT OF

HEALTH & HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

3311 Toledo Road

Hyattsville, MD 20782

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

FIRST CLASS
 

POSTAGE & FEES PAID
 

CDC/NCHS
 

PERMIT NO. G-284
 

07-0007 (2/2007)

CS107693

T27259

DHHS Publication No. (PHS) 2007-1417, Series 3, No. 33