NCHS Data Brief ■ No. 312 ■ June 2018

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Describing the Increase in Preterm Births in the 

United States, 2014–2016

Joyce A. Martin, M.P.H., and Michelle J.K. Osterman, M.H.S.

Key findings 

Data from the National 

Vital Statistics System

● The United States preterm

birth rate (births at less than

37 weeks of gestation per 100

total births) rose from 9.57% to

9.85% during 2014–2016.

● The increase in the total

preterm birth rate largely

reflects an increase among late

preterm births (34–36 weeks),

and in particular, among births

occurring at 36 weeks.

● Total and late preterm birth

rates rose 4% among births

in singleton deliveries. Total

and late preterm births also

increased among multiple

births during 2014–2016.

● Total and late preterm

rates rose among births 

to non-Hispanic white, 

non-Hispanic black, and 

Hispanic women. Early preterm 

births (less than 34 weeks) also 

increased among non-Hispanic 

black women.

● Preterm birth rates increased

in 23 states and the District of 

Columbia during 2014–2016.

Infants born before 37 weeks of gestation, commonly referred to as preterm, 

are at greater risk of early death than those born later in pregnancy and can 

suffer numerous health and developmental problems, especially at earlier 

gestational ages (1–3). The incidence of preterm birth in the United States 

rose from the early 1980s through 2006 but declined from 2007 through 2014 

(4–6). Recent data for 2014–2016, however, indicate that the preterm rate is 

on the rise again (6). This report describes trends in total, early (less than 34 

weeks), and late (34–36 weeks) preterm births by plurality, race and Hispanic 

origin of the mother, and state of residence during 2014–2016.

Keywords: plurality • race and Hispanic origin • state • National Vital 

Statistics System

Total preterm and late preterm birth rates rose from 2014 

through 2016.

Figure 1. Preterm birth rates: United States, 2014–2016

1

Significantly increasing linear trend for 2014–2016 (p < 0.05). 2

Significant increase from 2014 and 2015 (p < 0.05). 

NOTES: Figures may not add to totals because of rounding. Access data table for Figure 1 at: 

https://www.cdc.gov/nchs/data/databriefs/db312_table.pdf#1. 

SOURCE: NCHS, National Vital Statistics System, Natality. Percent

10

8

6

4

2

0

Less than 

34 weeks

34 weeks

35 weeks

36 weeks

2015

6.87 

9.63

3.73

1.86

1.28

2.76

2016

1

7.09

1

9.85

2

1.90

1

1.32

1

3.86

2.76

2014

6.82

9.57

3.69

1.87

1.27

2.75

Total preterm

Early preterm

Late preterm
NCHS Data Brief ■ No. 312 ■ June 2018

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● During 2014–2016, the preterm birth rate rose 3% in the United States, from 9.57% in 2014 

to 9.63% in 2015 to 9.85% in 2016 (Figure 1).

● The rate of late preterm births rose 4% from 2014 (6.82%) through 2016 (7.09%), with the 

largest rise occurring among infants delivered at 36 weeks, from 3.69% in 2014 to 3.86% in 

2016. Rates also increased at 34 (1.27% in 2014 to 1.32% in 2016) and 35 (1.87% to 1.90%) 

weeks.

● The rate of early preterm births was essentially unchanged for 2014–2016 (2.75%–2.76%).

● The increase in the total preterm rate for 2014–2016 largely reflects the increase in late 

preterm births, and in particular, births occurring at 36 weeks.

Births in both singleton and multiple deliveries were more likely to be 

preterm and late preterm in 2016 than in 2014.

● The preterm birth rate rose 4% among singleton births for 2014–2016, from 7.74% to 8.02% 

(Figure 2). 

● The singleton late preterm rate also increased 4% (from 5.67% to 5.92%). A smaller increase 

occurred in early preterm singleton births (from 2.07% to 2.10%).

Figure 2. Preterm birth rates, by plurality: United States, 2014–2016

Late preterm

Early preterm

2014 2015 2016 2014 2015 2016

21.22

1

39.82

1

61.04

21.43

60.30

38.86

21.38

59.99

38.61

2.09

5.73

7.82 

2.07

5.67

7.74 

1

2.10

1

5.92

1

8.02

1

Significantly increasing linear trend for 2014–2016 (p < 0.05) 

NOTES: Preterm is less than 37 weeks, late preterm is 34–36 weeks, and early preterm is less than 34 weeks of gestation. Figures may not add to totals because 

of rounding. Access data table for Figure 2 at: https://www.cdc.gov/nchs/data/databriefs/db312_table.pdf#2.

SOURCE: NCHS, National Vital Statistics System, Natality. Percent

70

60

50

30

20

10

0

40

Singleton births Multiple births
NCHS Data Brief ■ No. 312 ■ June 2018

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● Among multiple births, the preterm rate increased from 59.99% in 2014 to 61.04% in 2016, 

a rise of 2%. The late preterm rate for multiple births rose from 38.61% to 39.82%, and the 

early preterm rate was essentially stable (21.22% in 2016).

Total and late preterm birth rates rose for each of the largest race and 

Hispanic-origin groups during 2014–2016.

● Among infants born to non-Hispanic white women, the preterm rate was essentially 

unchanged from 2014 to 2015 but rose 2% from 2015 to 2016 (from 8.88% to 9.06%). 

The increase during 2014–2016 was among late preterm births, from 6.55% to 6.72%; the 

observed decline in early preterm births was not significant (Figure 3).

● The preterm rate among births to non-Hispanic black women rose from 2014 to 2015 

(13.23% to 13.41%) and again in 2016 (13.64%) for a total increase of 3%. Rates increased 

for both late preterm (8.47% in 2014 to 8.79% in 2016) and early preterm (4.76% to 4.86%) 

births.

● The preterm rate rose 5% among births to Hispanic mothers during 2014–2016 (from 9.03% 

to 9.45%); this rise is primarily attributable to the increase in late preterm births, from 

6.53% to 6.92%. The observed increase in the early preterm birth rate was not significant.

Figure 3. Preterm birth rates, by race and Hispanic origin of mother: United States, 2014–2016 Percent

16

14

12

8

6

4

2

0

10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

Significant increase from 2014 and 2015 (p < 0.05). 2

Significantly increasing linear trend for 2014–2016 (p < 0.05).

NOTES: Preterm is less than 37 weeks, late preterm is 34–36 weeks, and early preterm is less than 34 weeks of gestation. Figures may not add to totals because 

of rounding. Access data table for Figure 3 at: https://www.cdc.gov/nchs/data/databriefs/db312_table.pdf#3. 

SOURCE: NCHS, National Vital Statistics System, Natality. 
NCHS Data Brief ■ No. 312 ■ June 2018

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Rates of preterm births rose in about one-half of all states for 2016 

compared with 2014.

● Preterm birth rates were up in 23 states and the District of Columbia from 2014 through 

2016; increases in an additional 22 states were not statistically significant (Figure 4). 

● The preterm birth rate declined in Wyoming: nonsignificant declines were observed in three 

states—Montana, New Hampshire, and Pennsylvania. The rate for Iowa was unchanged.

Figure 4. Percent change in preterm birth rates, by state: United States, 2014 and 2016

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTES: Preterm is less than 37 weeks of gestation. Increases and decreases are significantly different at p < 0.05. Access data table for Figure 4 at: 

https://www.cdc.gov/nchs/data/databriefs/db312_table.pdf#4. 

SOURCE: NCHS, National Vital Statistics System, Natality.
NCHS Data Brief ■ No. 312 ■ June 2018

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Summary

The rise in preterm births in the United States for 2014 through 2016 largely reflects an increase 

among late preterm births, and more specifically, among births delivered at 36 weeks; the small 

change in the rate of early preterm births (2.75%–2.76%) was not statistically significant. The 

increase in late preterm births occurred among several groups, including both singleton and 

multiple deliveries and among each of the three largest race and Hispanic-origin groups. An 

earlier report demonstrated that late preterm rates also increased among women of all age groups 

during this period (7).

Although the rate of early preterm births, the infants at greater risk of poor outcomes, was 

essentially stable among all births for 2014 through 2016, rates increased among infants born in 

singleton deliveries and among births to non-Hispanic black mothers.

The latest provisional information from the National Center for Health Statistics Rapid Release 

program shows a continuing increase in total and late preterm birth rates and a stable early 

preterm birth rate for all births through 2017 (8).

Definitions

Preterm birth rate: The number of births delivered at less than 37 completed weeks of gestation 

per 100 total births, based on the obstetric estimate of gestation.

Early preterm birth rate: The number of births delivered at less than 34 completed weeks of 

gestation per 100 total births, based on the obstetric estimate of gestation.

Late preterm birth rate: The number of births delivered at 34–36 completed weeks of gestation 

per 100 total births, based on the obstetric estimate of gestation.

Birth rate at 34, 35, and 36 weeks: The number of births delivered at the specified completed 

weeks of gestation per 100 total births, based on the obstetric estimate of gestation.

Singleton births: Births in single-gestation pregnancies.

Multiple births: Births in multiple-gestation pregnancies (i.e., twin and triplet and higher-order 

births).
NCHS Data Brief ■ No. 312 ■ June 2018

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Data source and methods

This report is based on 2014–2016 data from the Natality Data File from the National Vital 

Statistics System (NVSS). The vital statistics natality file is derived from birth certificates and 

includes information for all births occurring in the United States. It is the primary data set for 

analyzing birth trends and patterns in the United States and is available at: 

https://www.cdc.gov/nchs/data_access/vitalstatsonline.htm.

Gestational age is based on the obstetric estimate of gestation (5). Race and Hispanic origin are 

self-reported by the mother and are based on bridged-race categories (4). Data by state are based 

on the mother’s place of residence.

References to increases or decreases in preterm birth rates indicate that differences are 

statistically significant at p < 0.05 based on a z test for difference in proportions. References to 

decreasing or increasing trends are statistically significant at the 0.05 level and assessed using the 

Cochran–Armitage test for trends, a modified chi-squared test.

About the authors

Joyce A. Martin and Michelle Osterman are with the National Center for Health Statistics, 

Division of Vital Statistics, Reproductive Statistics Branch.
NCHS Data Brief ■ No. 312 ■ June 2018

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References

1. Mathews TJ, MacDorman MF, Thoma ME. Infant mortality statistics from the 2013 period 

linked birth/infant death data set. National Vital Statistics Reports; vol 64 no 9. Hyattsville, MD: 

National Center for Health Statistics. 2015. Available from: https://www.cdc.gov/nchs/data/nvsr/

nvsr64/nvsr64_09.pdf.

2. Behrman RE, Butler AS, editors. Preterm birth: Causes, consequences, and prevention. 

Institute of Medicine Committee on Understanding Premature Birth and Assuring Healthy 

Outcomes. Washington, DC: National Academies Press. 2007.

3. Blencowe H, Cousens S, Chou D, Oestergaard M, Say L, Moller AB, et al. Born too soon: 

The global epidemiology of 15 million preterm births. Reprod Health 10 Suppl 1:S2. 2013.

4. Martin JA, Hamilton BE, Osterman MJK, Curtin SC, Mathews TJ. Births: Final data for 

2013. National Vital Statistics Reports; vol 64 no 1. Hyattsville, MD: National Center for Health 

Statistics. 2015. Available from: https://www.cdc.gov/nchs/data/nvsr/nvsr64/nvsr64_01.pdf. 

5. Martin JA, Osterman MJK, Kirmeyer SE, Gregory ECW. Measuring gestational age in vital 

statistics data: Transitioning to the obstetric estimate. National Vital Statistics Reports; vol 64 

no 5. Hyattsville, MD: National Center for Health Statistics. 2015.

6. Martin JA, Hamilton BE, Osterman MJK, Driscoll AK, Drake P. Births: Final data for 2016. 

National Vital Statistics Reports; vol 67 no 1. Hyattsville, MD: National Center for Health 

Statistics. 2018. Available from: https://www.cdc.gov/nchs/data/nvsr/nvsr67/nvsr67_01.pdf. 

7. Martin JA, Hamilton BE, Osterman MJK. Births in the United States, 2016. NCHS Data 

Brief, no 287. Hyattsville, MD: National Center for Health Statistics. 2017.

8. Hamilton BE, Martin JA, Osterman MJK, Driscoll AK, Rossen LM. Births: Provisional 

data for 2017. Vital Statistics Rapid Release; no 4. Hyattsville, MD: National Center for Health 

Statistics. May 2018.
NCHS Data Brief ■ No. 312 ■ June 2018

Suggested citation

Martin JA, Osterman MJK. Describing 

the increase in preterm births in the 

United States, 2014–2016. NCHS Data 

Brief, no 312. Hyattsville, MD: National 

Center for Health Statistics. 2018.

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

Charles J. Rothwell, M.S., M.B.A., Director

Jennifer H. Madans, Ph.D., Associate 

Director for Science

Division of Vital Statistics

Delton Atkinson, M.P.H., M.P.H., P.M.P., 

Director 

Hanyu Ni, Ph.D., M.P.H., Associate Director 

for Science

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