NCHS Data Brief ■ No. 80 ■ January 2012

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Three Decades of Twin Births in the United States, 1980–2009 

Joyce A. Martin, M.P.H.; Brady E. Hamilton, Ph.D.; and Michelle J.K. Osterman, M.H.S.

Key findings

•	 In 2009, 1 in every 30 babies 

born in the United States was a 

twin, compared with 1 in every 

53 babies in 1980.

•	 The twin birth rate rose 76 

percent from 1980 through 

2009, from 18.9 to 33.3 per 

1,000 births.

•	 If the rate of twin births 

had not changed since 1980, 

approximately 865,000 fewer 

twins would have been born in 

the United States over the last 

three decades.

•	 Twinning rates rose by at 

least 50 percent in the vast 

majority of states and the 

District of Columbia.

•	 Over the three decades, 

twin birth rates rose by nearly 

100 percent among women 

aged 35–39 and more than 200 

percent among women aged 40 

and over. 

•	 The older age of women at 

childbirth in 2009 compared 

with three decades earlier 

accounts for only about onethird of the rise in twinning 

over the 30 years.

The incidence of multiple births in the United States was quite stable at about 

2 percent of all births from 1915 (the earliest year for which reliable data are 

available) through the 1970s (1–3). By the early 1980s, however, twinning 

rates, and those for triplet and higher-order multiples (triplet/+) began to rise 

(3,4), ultimately leading to what has been called “an epidemic of multiple 

pregnancies” (5). The marked increase in multiple births is important for 

reasons beyond their relative rarity. Plural pregnancies tend to exact a greater 

toll on the health of the mother (6,7), and outcomes for births in multiple 

deliveries are often compromised compared with singletons (6,7). The rise 

in the rate of twins, which comprise the majority of multiples (96 percent in 

2009), has had an unfavorable impact on key indicators of perinatal health 

such as rates of preterm birth and low birthweight (8). This report describes 

U.S. trends in births in twin deliveries for the 30-year period 1980–2009. 

Keywords: National Vital Statistics System • race and Hispanic origin • statespecific rates

One in every 30 infants born in 2009 was a twin. 

0

5

10

15

20

25

30

35

0

20

40

60

80

100

120

140

160

Per 1,000 births

Births in thousands

Year

1980 1984 1988 1992 1996 2000 2004 2008

2009

Rate

Number

Figure 1. Number and rate of twin births: United States, 1980–2009

SOURCE: CDC/NCHS, National Vital Statistics System.
NCHS Data Brief ■ No. 80 ■ January 2012

■  2  ■

•	 The number of twin births more than doubled from 1980 through 2009, rising from 68,339 to 

more than 137,000 births in each year from 2006 to 2009. In 1980, 1 in every 53 babies born in 

the United States was a twin, compared with 1 in every 30 births in 2009 (Figure 1). 

•	 Over the three decades, the twin birth rate rose by 76 percent, from 18.9 to 33.2 per 1,000 

births (or from 1.9 percent to 3.3 percent of all births) (Figure 1). 

•	 Increases in the twin birth rate averaged more than 2 percent a year from 1980 through 2004 

(peaking at more than 4 percent from 1995 to 1998). From 2005 to 2009, however, the pace of 

increase slowed to less than 1 percent annually.

•	 If the rate of twin births had not changed from the 1980 level, approximately 865,000 fewer 

twins would have been born in the United States over the three decades.

Twin birth rates increased in all states from 1980 through 2009. 

DC

MT

WY

ID

WA

OR

NV

UT CA

AZ

ND

SD

NE

CO

NM

TX

OK

KS

AR

LA

MO

IA

MN

WI

IL IN

KY

TN

MS AL GA

FL

SC

NC

VA WV

OH

MI

NY

PA

MD

DE

NJ

CT

RI

MA

ME

VT

NH

AK

HI

Figure 2. Percentage increase in twin birth rates: United States and each state, 1980–2009

Total U.S.

increase:

76.0% 

75.0%–99.9%

100.0% and

greater

50.0%–74.9%

Less than 50.0%

NOTES: The change in the twin birth rate for New Mexico is based on data years 1982–2009. Access data table for Figure 2 at: 

http://www.cdc.gov/nchs/data/databriefs/db80_tables.pdf.

SOURCE: CDC/NCHS, National Vital Statistics System.

•	 Increases in twin birth rates are seen in all 50 states and the District of Columbia over the three 

decades. Rates rose by at least 50 percent in 43 states and the District of Columbia, and by more 

than 100 percent in five states (Connecticut, Hawaii, Massachusetts, New Jersey, and Rhode

Island) (Figure 2). 

•	 Twinning rates differed widely by state in 2009. Rates ranged from a low of 22.3 per 1,000 

births in New Mexico (2 percent of births), to a high of 45.9 in Connecticut (nearly 5 percent of

births). 
NCHS Data Brief ■ No. 80 ■ January 2012

■  3  ■

Twin birth rates doubled among non-Hispanic white mothers over the three 

decades. 

Figure 3. Twin birth rates, by race and Hispanic origin of mother: United States, 1980, 1990, 2000, and 2009

1980 1990 2000 2009

Per 1,000 births

All races Non-Hispanic white Non-Hispanic black Hispanic

0

5

10

15

20

25

30

35

40

18.9

22.6

29.3

33.2

18.3

23.5

32.3

37.0

24.2

26.7

33.4

38.0

16.8 18.0

20.2

22.5

NOTE: 1980 data by race and Hispanic origin are based on a 22-state reporting area representing approximately 90% of births for that year.

SOURCE: CDC/NCHS, National Vital Statistics System.

•	 Twin birth rates rose among each of the three largest race and Hispanic origin groups from

1980 through 2009. Rates doubled among non-Hispanic white mothers, rose by about one-half

among non-Hispanic black mothers, and by one-third among Hispanic mothers (Figure 3). 

•	 Twinning rates historically have been higher among non-Hispanic black women (4). The 

difference has narrowed over the three decades, however, as twinning rates for non-Hispanic

white mothers have risen at a greater pace. In 2009, the twinning rate for non-Hispanic black

mothers (38.0 per 1,000) was only slightly higher than that for non-Hispanic white mothers

(37.0). 

•	 Hispanic mothers continue to be less likely to bear twins. In 2009, their rate (22.5 per 1,000)

was about two-thirds that of non-Hispanic white and non-Hispanic black women.

Twinning rates rose by more than 200 percent among women aged 40 and 

over. 

•	 Twin birth rates increased for women of all ages over the three decades, with the largest 

increases among women aged 30 and over. From 1980 to 2009, rates increased 76 percent for 

women aged 30–34, nearly 100 percent for women aged 35–39, and more than 200 percent for 

women aged 40 and over (Figure 4). 

•	 Historically, twin birth rates have risen with advancing age, peaking at 35–39 years and

declining thereafter (4). Since 1997, however, rates have been highest among women in their 40s. 

•	 In 2009, 7 percent of all births to women aged 40 and over were born in a twin delivery 

compared with 5 percent of births to women aged 35–39, and 2 percent of births to women under 

age 25. 
NCHS Data Brief ■ No. 80 ■ January 2012

■  4  ■

Figure 4. Twin birth rates, by age of mother: United States, 1980 and 2009

Age of mother in years

1980 2009

Per 1,000 births

All ages Under 20 20–24 25–29 30–34 35–39 40 and over

0

10

20

30

40

50

60

70

80

SOURCE: CDC/NCHS, National Vital Statistics System.

18.9

33.2

12.8

16.3 17.4

23.3 20.5

30.6

23.5

41.4

25.3

49.9

22.1

71.0

The age distribution of women giving birth changed over the three 

decades. 

•	 Over this 30-year period (1980–2009), the overall age distribution of women giving birth in the 

United States shifted—a result of delayed childbearing and an older female population. In 1980, 

women aged 30 and over accounted for about 20 percent of all births (i.e., singletons, twins, and 

higher-order multiples), compared with more than 35 percent for 2000–2009 (Figure 5). 

•	 The increasingly older age of mothers over the decades would be expected to influence twin

birth rates because of the higher spontaneous (i.e., without the use of fertility therapies) twinning 

rates of women in their 30s. 

Figure 5. Distribution of all births, by age of mother: United States, 1980 and 2009

Year

Percent

30 and over

1980 2009

0

20

40

60

80

100 40 and over

35–39

30–34

25–29

20–24

Under 20

SOURCE: CDC/NCHS, National Vital Statistics System.
NCHS Data Brief ■ No. 80 ■ January 2012

■  5  ■

Older maternal age accounts for only about one-third of the rise in twinning 

over the 30 years. 

•	 The older maternal age distribution explains only some of the increase in the twinning rate. If 

this distribution had not changed (that is, the age distribution of women giving birth in 2009 was 

similar to that in 1980), the twin birth rate would be only 14 percent lower (28.6 compared with 

33.2 per 1,000); that is, older maternal age accounts for only part, or about one-third of the total 

rise in the twin birth rate over the study period (Figure 6).

•	 Another factor related to the rise in twinning in recent years is the increased use of infertility 

treatments, both assisted reproductive technologies (ART) (e.g., in vitro fertilization) and nonART treatments (ovulation stimulation medications without ART) (9,10). The use of these 

therapies became more prevalent during the 1980s and 1990s and is more common among 

women aged 30 and over (11).

•	 Much of the rise in twinning over the three decades not accounted for by the older maternal

age distribution, or about two-thirds of the increase in the twin birth rate from 1980 to 2009, is 

likely associated with these therapies (9,10).

Figure 6. Observed and age-adjusted twin birth rates: United States, 1980 and 2009

Observed Age adjusted1

1980 2009 2009

18.9

33.2

28.6

Per 1,000 births

14% lower

0

5

10

15

20

25

30

35

40

1

The 1980 U.S. maternal age distribution was used as the standard population.

SOURCE: CDC/NCHS, National Vital Statistics System.
NCHS Data Brief ■ No. 80 ■ January 2012

■  6  ■

Summary

The number of twins has doubled and the rate of twin births has risen by more than three-fourths 

over the three decades 1980–2009. Increases in twin birth rates averaged more than 2 percent 

annually from 1980 to 2004, but the pace of increase slowed to less than 1 percent from 2005 

to 2009. The increase in twinning over the three decades has been widespread, occurring across 

age and race and Hispanic origin groups, and in all states within the United States. The largest

increases have been among non-Hispanic white women and mothers aged 30 and over.

Older maternal age accounts for about one-third of the growth in the twinning rate over this 

period. The increased availability and use of infertility treatments likely explains much of the 

remainder of the rise (9,10). Similar increasing trends in multiple births associated with both 

maternal age and infertility therapies have been observed in Western Europe and other countries 

during the 1980s and 1990s (10,12). 

The study of multiple births is important because of their elevated health risks and accompanying 

greater health care costs (6). The rise in twinning has influenced the upward trend in key infant

health indicators such as preterm and low birthweight rates during the 1980s and 1990s (8). An 

estimated additional 865,000 twins were born in the United States over the study period due to 

rising rates; more than one-half of these infants were low birthweight, and 1 in 10 were very low 

birthweight (3,4,13). New information soon to be available from the 2003 revision of the U.S.

Standard Certificate of Live Birth and the U.S. Standard Report of Fetal Death on topics such as

use of infertility treatment and admission to a neonatal intensive care unit, will further expand 

understanding of the causes and risks of multiple-gestation pregnancies. 

Definitions

Twin birth: Refers to individual live birth in a twin pregnancy; does not include births in triplet 

and higher order multiple-gestation pregnancies.

Twin birth rate: Refers to the number of twin births per 1,000 total births.

Data sources and methods

This report contains data from the Natality Data File from the National Vital Statistics System.

The vital statistics natality file includes information on a wide range of maternal and infant

demographic and health characteristics for all births occurring in the United States. 

Direct standardization was used to estimate the effect of the changing maternal age distribution 

on twin birth rates over the study period. The 1980 distribution of births by age of mother is used 

as the standard population. The impact of the age adjustment on the relative change in the twin 

birth rate from 1980 to 2009 is calculated as the difference between the 2009 observed and ageadjusted rate twin birth rates over the difference between the 1980 and 2009 observed rates.

The additional number of twins born as the result of rising twin birth rates is calculated by 

applying the 1980 twin birth rate to the total number of births for each year during 1981–2009 

and subtracting from the observed number of 2009 twin births. 
NCHS Data Brief ■ No. 80 ■ January 2012

■  7  ■

Information on births of Hispanic origin for 1980 was available for a 22-state reporting area:

Arizona, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Illinois, Indiana, Kansas,

Maine, Mississippi, Nebraska, Nevada, New Jersey, New Mexico, New York, North Dakota,

Ohio, Texas, Utah, and Wyoming. These states accounted for 57 percent of all U.S. births in 1980, 

an estimated 57 percent of births to non-Hispanic white and non-Hispanic black mothers, and 90

percent of all births to Hispanic mothers. The twin birth rate for New Mexico is based on 1982

data; information by plurality for New Mexico was not reliable for 1980 and 1981.

About the authors

Joyce A. Martin, Brady E. Hamilton, and Michelle J.K. Osterman are with the Centers for Disease

Control and Prevention’s National Center for Health Statistics, Division of Vital Statistics,

Reproductive Statistics Branch.

References

1. National Center for Health Statistics. Vital Statistics of the United States, 1917–1993.

Available from: http://www.cdc.gov/nchs/products/vsus.htm. 

2. National Center for Health Statistics. Vital statistics rates in the United States, 1940–1960.

Washington, DC: U.S. Department of Health, Education, and Welfare, Public Health Service.

1968.

3. Taffel SM. Health and demographic characteristics of twin births: United States, 1988.

National Center for Health Statistics. Vital Health Stat 21(50). 1992.

4. Martin JA, Park MM. Trends in twin and triplet births: 1980–97. National vital statistics

reports; vol 47 no 24. Hyattsville, MD: National Center for Health Statistics. 1999.

5. Newman RB, Luke B. Multifetal pregnancy: A handbook for care of the pregnant patient.

Philadelphia, PA: Lippincott William & Wilkins. 2000.

6. The ESHRE Capri Workshop Group. Multiple gestation pregnancy. Hum Reprod 15(8):1856–

64. 2000.

7. Luke B, Brown MB. Contemporary risks of maternal morbidity and adverse outcomes with

increasing maternal age and plurality. Fertil Steril 88(2):283–93. 2007.

8. Blondel B, Kogan MD, Alexander GR, Dattani N, Kramer MS, Macfarlane A, Wen SW.

The impact of the increasing number of multiple births on the rates of preterm birth and low 

birthweight: An international study. Am J Pub Health 92(8):1323–30. 2002.

9. Reynolds MA, Schieve LA, Martin JA, Jeng G, Macaluso M. Trends in multiple births

conceived using assisted reproductive technology, United States, 1997–2000. Pediatrics 111(5 

Part 2):1159–66. 2003.

10. Blondel B, Kaminski M. Trends in the occurrence, determinants, and consequences of

multiple births. Semin Perinatol 26(4):239–49. 2002.

11. Chandra A, Stephen EH. Infertility service use among U.S. women: 1995 and 2002. Fertil

Steril 93(3):725–36. 2010.
NCHS Data Brief ■ No. 80 ■ January 2012

12. Imaizumi Y. Trends of twinning rates in ten countries, 1972–1996. Acta

Genet Med Gemellol (Roma) 46(4):209–18. 1997.

13. Martin JA, Hamilton BE, Ventura SJ, et al. Births: Final data for 2009.

National vital statistics reports; vol 60 no 1. Hyattsville, MD: National

Center for Health Statistics. 2011.

Suggested citation

Martin JA, Hamilton BE, Osterman MJK.

Three decades of twin births in the United 

States, 1980–2009. NCHS data brief, no 80.

Hyattsville, MD: National Center for Health

Statistics. 2012.

Copyright information

All material appearing in this report is in 

the public domain and may be reproduced 

or copied without permission; citation as to 

source, however, is appreciated.

National Center for Health 

Statistics

Edward J. Sondik, Ph.D., Director

Jennifer H. Madans, Ph.D., Associate 

Director for Science

Division of Vital Statistics

Charles J. Rothwell, M.S., Director

U.S. DEPARTMENT OF

HEALTH & HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

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