Preterm Births
Updated: March 2015
Preterm Births
March 2015
Infants born preterm are at increased risk for a number of health problems. Births
occurring at least three weeks before an infant’s due date — earlier than the 37th
week of pregnancy—and especially late preterm births, increased markedly
between 1990 and 2006, but have since decreased.
Importance
In 2010, more than a third of infant deaths were from complications related to preterm births, making
prematurity the most frequent cause of infant mortality.1,2 Infants born preterm have higher rates of health
complications and lifelong disabilities, including mental retardation, learning and behavioral problems,
cerebral palsy, lung problems, vision and hearing loss, diabetes, high blood pressure, and heart disease. 3
Children born preterm may also have increasing difficulties with complex language functions between the
ages of three and 12 years.4 Children born moderately preterm are more likely than full-term infants to have
lower intelligence and poorer visual-motor skills and executive functioning at age seven.5 Even among
children born at term, one recent study finds earlier gestational age is associated with lower reading and
math scores at third grade.6 There is some evidence linking preterm births with symptoms of autism.7,8
Babies born before the 34th week of pregnancy, very or moderately preterm, have the highest risk for early
death and enduring health problems, but recent research has shown than even late preterm infants (at 34 to
36 weeks of pregnancy) have greater health risks than full-term babies.9
The underlying causes of preterm birth are poorly understood, although genetic, social, and environmental
factors all likely play a role.10 Women with a previous premature birth, a multiple pregnancy (twins, triplets,
or more), certain cervical or uterine abnormalities, and a number of medical conditions are at increased risk
of preterm birth. Lifestyle factors also can elevate risk: these include late or no prenatal care, cigarette
smoking, alcohol and illicit drug use, domestic violence, very high stress levels, and prolonged work hours
involving standing. 11 Maternal depression during pregnancy may be another risk factor for preterm birth.12
Notably, however, about one-half (46 percent, in 2013) of premature births involve cesarean section.13 Most
of these procedures are in response to pregnancy complications or indicated health problems in the mother
or fetus; however, some may occur without good medical justification, to suit preferences of the mother or
attending physician. In addition, the fact that normal-term babies born by cesarean section are twice as likely
as infants born vaginally to have respiratory problems (which are often signs of prematurity), may be related
to the difficulty of accurately establishing a date of conception.14
2
Preterm Births
March 2015
Trends
The U.S. preterm birth rate rose by more than 20 percent between 1990 and 2006, accounting for nearly
one in eight births (12.8 percent) in 2006. Most of this increase was accounted for by the rise in the rate of
late preterm births, which rose by 25 percent during this period. However, since then, the preterm birth rate
has fallen by ten percent, and was at 11.4 percent in 2013. (Figure 1)
Figure 1
All Preterm and Late Preterm Births, as Percentage of All Births,
1990-2013
25
All Preterm Births (<37 wks. gestation)
Late Preterm (34-36 wks. gestation)
Percent of all births
20
Preterm: Singleton births only
15
12.8
11.6
11.3
11.1
10.6
10
9.6
10.1
9.7
9.1
8.2
7.3
8.0
5
0
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
2015
Note: Percentage calculations exclude records missing gestation period data.
Data for 1990-1995: Centers for Disease Control and Prevention, National Center for Health Statistics, National Vital
Statistics System. VitalStats online tool. Available at
www.cdc.gov/nchs/data_access/vitalstats/VitalStats_Births.htm. Data for 1995 -2013: Centers for Disease Control
and Prevention, National Center for Health Statistics, CDC Wonder online database. Available at:
http://wonder.cdc.gov/natality.html
3
Preterm Births
March 2015
Differences by Gestation Period
In 2013, about 70 percent of preterm births were late preterm (34-36 weeks gestation); another 13 percent
were moderately preterm (33-34 weeks); and 17 percent were very preterm (less than 32 weeks). The
increase in preterm births between 1990 and 2006 is mostly accounted for by the rise in late preterm births,
which (as a proportion of all births) rose from 7.3 to 9.1 percent—an increase by more than one-quarter.
Similarly, the recent decrease in preterm births is also mostly accounted for by a decrease in late preterm
births, which fell from 9.1 to 8.0 percent between 2006 and 2013. (Figure 1)
Differences by Race and Hispanic Origin15
Black women have the highest rates of preterm births (16.3 percent in 2013), followed by American Indians
(13.1 percent), Hispanics (11.3 percent), whites and Asian/Pacific Islanders (10.2 percent, each). (Figure 2)
Figure 2
Percentage Preterm Births, by Race/Hispanic Origin1,
2014*
25.0
The gap between blacks
and whites decreased
between 1990 and 2004,
but has remained steady
Percent of All Births
20.0
since then, at around
15.0
seven percentage points.
13.2
The gap between whites
10.2
10.0
9.0
8.9
and Hispanics decreased
8.5
between 1990 and 2006,
5.0
but has since increased.
(Appendix 1)
0.0
Figure
3
Non-HispanicPreterm
Black
Hispanic
Asian or Pacific2014*
American Indian
Percentage
Births,
by Plurality,
Non-Hispanic White
Islander
120.0
1
Percent of All Births
Hispanics can be of any race.
Note: Percentage calculations exclude records missing gestation period data.
Source: : Centers for Disease Control and Prevention, National Center for Health Statistics, CDC Wonder online
database. Available at: http://wonder.cdc.gov/natality.html
100.0
*Based
on Obstetric/Clinical Gestation estimate
98.3
80.0
Differences
by Plurality
of Birth
58.7
60.0
Preterm births are more
likely to occur in the
40.0
context of multiple births
(twins, triplets, etc.). In
20.0
7.7
0.0
Singleton births
Twin
Note: Percentage calculations exclude records missing gestation period data.
Source: Centers for Disease Control and Prevention, National Center for Health Statistics, CDC Wonder online
database. Available at: http://wonder.cdc.gov/natality.html.
*Based on Obstetric/Clinical Gestation estimate
Triplet
4
Preterm Births
March 2015
2013 9.7 percent of singleton births were preterm, compared with 56.6 percent of twin births and 93.1
percent of triplet births. (Figure 3) While the numbers of multiple births have risen in the past two decades,
due in part to the use of fertility treatments and a greater number of older women bearing children, they
accounted for just over three percent of all U.S. births in 2013.16 The rate of preterm singleton births rose
from 9.7 percent in 1990, to 11.1 percent in 2006; it then fell to 9.7 percent in 2013. Similarly, the rate of
preterm twin births rose from 47.3 percent in 1990 to 60.1 in 2007, before falling to 56.6 in 2013. (Appendix
1)
5
Preterm Births
March 2015
Differences by Age of Mother
Preterm births are more likely among teen mothers and mothers forty and older. In 2013, 13 percent of
births to mothers under 20 years old were preterm, compared with 11 percent, each, to mothers ages 20 to
29 and 30 to 39, 16 percent to mothers 40 to 44, and 25 percent to mothers 45 and older. Increases since
1993 in the proportion of births that are preterm have been greatest among older mothers: nine percentage
points among mothers 45 and older, three percentage points among births to mothers ages 40-44, and one
percentage point among births to mothers ages 20 to 39. In contrast, the percentage of preterm births to
mothers younger than 20 has decreased by one percentage point since 1993. (Figure 4)
Figure 4
50.0
Percentage Preterm Births, by Age of Mother, 1 1994, 2004, and
2014
1994
2004
2014
40.0
Percent of All Births
30.0
25.6 25.3
20.0
14.2 14.5
16.1 15.7
13.1
10.4
11.9
10.8
12.5
10.5
17.4
13.5
11.3
10.0
0.0
Under 20 years
20 to 29 years
30 to 39 years
40 to 44 years
45 years or older
1In
1994, data includes mothers up to age 49, in 2004 and 2014, data includes mother up to age 54.
Note: Percentage calculations exclude records missing gestation period data.
Source: Data for 1993: Centers for Disease Control and Prevention, National Center for Health Statistics,
National Vital Statistics System. VitalStats online tool. Available at
www.cdc.gov/nchs/data_access/vitalstats/VitalStats_Births.htm. Data for 2003 and 2013: Centers for Disease
Control and Prevention, National Center for Health Statistics, CDC Wonder online database.
6
Preterm Births
March 2015
State and Local Estimates

National Center for Health Statistics (NCHS) provides state-level data for 2013 by race, ethnicity,
plurality, and birthweight, at: http://www.cdc.gov/nchs/data/nvsr/nvsr64/nvsr64_01_tables.pdf
(table I-8)

Preliminary 2013 data for states (and some counties) are presented in the March of Dimes’ 2014
Premature Birth Report Card: http://www.marchofdimes.com/mission/prematurity-reportcard.aspx

State-level data on late preterm singleton birth rates for 1990-1991 and 2005-2006 are available in
an NCHS Data Brief, here: www.cdc.gov/nchs/data/databriefs/db24.pdf

Preterm births by state and in major cities for 1990-2012 are available from the Kids Count Data
Center, at: http://datacenter.kidscount.org/data/tables/18-preterm-births?loc=1&loct=2#detailed/2/252/false/868,867,133,38,35/any/279,280
International Estimates
A 2012 report published by the World Health Organization, Born Too Soon: The Global Action Report on
Preterm Birth, includes 2010 rates of preterm births for 184 countries, at
http://www.who.int/pmnch/media/news/2012/preterm_birth_report/en/index5.html. The U.S. ranks 130th
(where 1 designates the country with the lowest rate).
National Goals
Healthy People 2020, an initiative of the U.S. Department of Health and Human Services, includes a goal of
reducing preterm births from 12.7 percent in 2007 to 11.4 percent in 2020. There are also more specific
goals to reduce late, moderate, and very preterm births.
More information is available at: http://www.healthypeople.gov/2020/topics-objectives/topic/maternal-infantand-child-health/objectives (Objective MICH-9).
7
Preterm Births
March 2015
What Works to Make Progress on This Indicator
Women should consult their health care provider, both when contemplating pregnancy and after pregnancy
begins, in order to identify and treat potential risk factors early. Early and regular prenatal care is
recommended for all women.
Taking folic acid daily (at least 400 mg) for at least a year prior to becoming pregnant may cut the risk of
prematurity by half. Avoiding smoking, alcohol, and illicit drug use, as well as maintaining a healthy weight,
also lower the risk of preterm birth.
Medications may be prescribed to speed lung maturation in the fetus (corticosteroids), or to postpone labor
(tocolytics).
For women who have had a preterm singleton birth in the past, the American College of Obstetricians and
Gynecologists (ACOG) recommends progesterone shots to reduce the risk of a second preterm birth.17
A home-visiting program for very preterm infants, consisting of nine visits over the first year of life, and
focusing on topics of infant development, parent mental health, and the parent-infant relationship, was
associated, when children were age four, with lower caregiver anxiety, and reduced child internalizing
behaviors, compared with a group of preterm infants who did not receive the intervention. 18
Also, see Child Trends’ LINKS database (“Lifecourse Interventions to Nurture Kids Successfully”), for
reviews of many rigorously evaluated programs, including the following which have been shown to be
effective at preventing preterm births or improving outcomes:

CenteringPregnancy: www.childtrends.org/?programs=centeringpregnancy

Nurse-Family Partnership: www.childtrends.org/?programs=nurse-family-partnership

Early Intervention Program for Low Birth Weight Infants: www.childtrends.org/?programs=earlyintervention-program-for-low-birth-weight-infants

Infant Health and Development Program (IHDP): www.childtrends.org/?programs=infant-healthand-development-program-ihdp

Newborn Individualization Developmental Care and Assessment Program (NIDCAP):
www.childtrends.org/?programs=newborn-individualization-developmental-care-and-assessmentprogram-nidcap
Note: Child Trends does not provide medical advice or diagnosis. Readers are urged to consult with a
qualified health professional before embarking on any course of treatment.
8
Preterm Births
March 2015
Related Indicators

Low and Very Low Birthweight Infants: www.childtrends.org/?indicators=low-and-very-lowbirthweight-infants

Late or No Prenatal Care: www.childtrends.org/?indicators=late-or-no-prenatal-care

Mothers Who Smoke While Pregnant: www.childtrends.org/?indicators=mothers-who-smoke-whilepregnant
Definition
Length of gestation is measured as the interval between the first day of the mother’s last normal menstrual
period and the date of birth. Infants born prior to 37 full weeks’ gestation are considered preterm.
Data Sources

Data for 1995-2013: Centers for Disease Control and Prevention, National Center for Health
Statistics, CDC Wonder online database. Available at: http://wonder.cdc.gov/natality.html

Data for 1990-1995: Centers for Disease Control and Prevention, National Center for Health
Statistics, National Vital Statistics System. VitalStats online tool. Available at
www.cdc.gov/nchs/data_access/vitalstats/VitalStats_Births.htm
Raw Data Source
National Center for Health Statistics, National Vital Statistics System, birth data files.
www.cdc.gov/nchs/data_access/Vitalstatsonline.htm
9
Preterm Births
March 2015
Appendix 1 - Percentage of Births That Are Preterm, by Selected
Characteristics: Selected Years, 1990-2013
1990
1995
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
10.6
11.0
11.4
11.6
11.8
11.6
11.9
12.1
12.3
12.5
12.7
12.8
12.7
12.3
12.2
12.0
11.7
11.6
11.4
Very Preterm
(<32 wks. gestation)
1.9
1.9
1.9
2.0
2.0
1.9
1.9
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.9
1.9
1.9
Moderately Preterm
(32-33 wks. gestation)
1.4
1.4
1.5
1.5
1.5
1.5
1.5
1.5
1.6
1.6
1.6
1.6
1.6
1.6
1.5
1.5
1.5
1.5
1.5
Late Preterm
(34-36 wks. gestation)
7.3
7.7
8.0
8.1
8.3
8.2
8.5
8.6
8.8
8.9
9.1
9.1
9.0
8.8
8.7
8.5
8.3
8.1
8.0
8.5
9.4
9.9
10.2
10.5
10.4
10.8
11.0
11.3
11.5
11.8
11.7
11.5
11.1
10.9
10.8
10.5
10.3
10.2
18.9
17.8
17.6
17.6
17.6
17.4
17.6
17.7
17.8
17.9
18.4
18.5
18.3
17.5
17.5
17.1
16.8
16.5
16.3
11.0
10.9
11.2
11.4
11.4
11.2
11.4
11.6
11.9
12.0
12.1
12.2
12.3
12.1
12.0
11.8
11.7
11.6
11.3
9.8
9.9
10.2
10.4
10.4
9.9
10.3
10.4
10.5
10.5
10.8
10.9
10.8
10.6
10.8
10.7
10.4
10.2
10.2
11.6
12.4
12.2
12.2
12.9
12.7
13.2
13.1
13.5
13.7
14.1
14.2
14.1
13.8
13.6
13.6
13.5
13.3
13.1
9.7
9.8
10.0
10.1
10.3
10.1
10.4
10.4
10.6
10.8
11.0
11.1
11.0
10.6
10.4
10.3
10.1
9.9
9.7
Twin
47.3
52.2
54.3
55.5
56.6
56.1
56.8
57.6
58.7
59.1
60.0
60.0
60.1
58.9
58.7
57.8
57.3
56.7
56.6
Triplet
86.7
90.6
92.1
91.1
91.3
90.9
91.4
91.3
92.3
92.1
92.7
91.5
93.7
92.9
94.2
93.9
93.4
92.7
93.1
All Preterm Births
(<37 wks. gestation)
Race/Hispanic Origin
(Mother's)
1
White, Non-Hispanic
Black, Non-Hispanic
Hispanic
Asian or Pacific Islander
American Indian
Plurality
Singleton births
10
Preterm Births
March 2015
1990
1995
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
14.6
13.8
13.8
14.0
14.1
14.0
14.1
14.0
14.3
14.5
14.7
14.8
14.6
14.1
13.7
13.7
13.6
13.3
13.1
10.1
10.4
10.8
11.0
11.2
11.1
11.4
11.5
11.8
11.9
12.1
12.2
12.1
11.7
11.6
11.6
11.1
11.0
10.8
9.8
10.6
11.2
11.4
11.6
11.4
11.8
12.0
12.3
12.5
12.7
12.8
12.7
12.4
12.3
12.3
11.8
11.6
11.4
12.3
13.5
14.1
14.6
14.8
14.7
15.1
15.5
15.7
16.1
16.2
16.4
16.5
16.3
16.4
16.4
15.6
16.1
15.9
15.5
19.2
22.3
23.0
23.5
23.6
25.5
26.2
25.9
25.6
26.0
25.9
26.5
27.1
26.8
26.8
27.3
25.5
24.6
Age of Mother
Under 20 years
20 to 29 years
30 to 39 years
40 to 44 years
45 years or older
‘-‘ Indicates data are not available.
Note: Percentage calculations exclude records missing gestation period data.
1
Persons of Hispanic origin may be of any race.
Sources: Data for 1990-1995: Centers for Disease Control and Prevention, National Center for Health Statistics, National Vital Statistics System. VitalStats online tool. Available at
www.cdc.gov/nchs/data_access/vitalstats/VitalStats_Births.htm. Data for 1995-2013: Centers for Disease Control and Prevention, National Center for Health Statistics, CDC Wonder online database.
Available at: http://wonder.cdc.gov/natality.html.
11
Preterm Births
March 2015
Endnotes
1
Matthews, T. J. & MacDorman, M. F. (2013) Infant mortality statistics from the 2010 period linked birth/infant death data
set. National Vital Statistics Reports, 62(8). Hyattsville, MD: National Center for Health Statistics. Available at
http://www.cdc.gov/nchs/data/nvsr/nvsr62/nvsr62_08.pdf
2
Williamson, D.M., Abe, K., Bean, C., Ferré, C., et al. (2008). Current research in preterm birth. Journal of Women’s
Health, 17(10).
3
March of Dimes (2012). What we know about prematurity. Retrieved from
http://www.marchofdimes.com/mission/prematurity_indepth.html
4
van Noort, I. L., Franken, M-C. J. P., and Weisglas-Kuperus, N. (2012). Language functions in preterm-born children: A
systematic review and meta-analysis. Pediatrics, published online March 19, 2012.
5
Cserjesi, R., Van Braeckel, K. N. J. A., Butcher, P. R., Kerstjens, J. M., Rejneveld, S. A., Bouma, A., Geuze, R. H., &
Bos, A. F. (2012). Functioning of 7-year-old children born at 32 to 35 weeks’ gestational age. Pediatrics, 130(4) e838e846.
6
Noble, K. G., Fifer, W. P., Rauh, V. A., Nomura, Y., & Andrews, H. F. (2012). Academic achievement varies with
gestational age among children born at term. Pediatrics, 130(2), e257-e264.
7
Buchmayer, S., Johansson, S., Johansson, A., Hultman, C. M., Sparen, P., and Cnattingius, S. (2009). Can association
between preterm birth and autism be explained by maternal or neonatal morbidity? Pediatrics, 124(5), e817-e835.
8
Pinto-Martin, J. A., Levy, S. E., Feldman, J. F., Lorenz, J. M., Paneth, N. and Whitaker, A. H. (2011). Prevalence of
autism spectrum disorder in adolescents born weighing <2000 grams. Pediatrics, published online, October 17, 2011.
9
Martin, J. A., Hamilton, B. E., et al., (2009) Op. cit.
10
Williamson, D.M., Abe, K., Bean, C., Ferré, C., et al. Op. cit.
11
March of Dimes, Op. cit.
12
Straub, H., Adams, M, Kim, J. J., & Silver, R. K. (2012). Antenatal depressive symptoms increase the likelihood of
preterm birth. American Journal of Obstetrics & Gynecology, 207(4), 329.e1-329.e4.
13
United States Department of Health and Human Services (US DHHS), Centers for Disease Control and Prevention
(CDC), National Center for Health Statistics (NCHS), Division of Vital Statistics. (2014).Natality public-use data 20072020, on CDC WONDER Online Database. Accessed at http://wonder.cdc.gov/natality-current.html
12
Preterm Births
March 2015
14
Engle, W. A., Kominiarek, M. A. (2008). Late preterm infants, early preterm infants, and timing of elective deliveries.
Clinics in Perinatology, 35, 325-341.
15
Hispanics may be of any race. Estimates for whites and blacks in this report do not include Hispanics.
16
United States Department of Health and Human Services (US DHHS), Centers for Disease Control and Prevention
(CDC), National Center for Health Statistics (NCHS), Division of Vital Statistics. (2014).Natality public-use data 20072020, on CDC WONDER Online Database. Accessed at http://wonder.cdc.gov/natality-current.html
17
The American Congress of Obstetricians and Gynocologists, Committee on Obstetric Practice. (2011). Use of
progesterone to reduce preterm birth. ACOG Committee Opinion, 419. The Society for Maternal Fetal Medicine
Publications Committee. Available at:
http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Obstetric_Practice/Use_of_Proge
sterone_to_Reduce_Preterm_Birth
18
Spencer-Smith, M M., Spittle, A. J., Doyle, L. W., Lee, K. J., Lorefice, L., Suetin, A., Pascoe, L., & Anderson, P. J.
(2012). Long-term benefits of home-based preventive care for preterm infants: A randomized trial. Pediatrics. Published
online November 5, 2012.
13