NCHS Data Brief ■ No. 155 ■ June 2014

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Recent Declines in Induction of Labor by Gestational Age

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

Key findings

Data from the Natality 

Data File, National Vital 

Statistics System

• After nearly 20 years 

of consecutive increases, 

induction of labor for singleton 

births reached a high of 23.8% 

in 2010, then declined in 2011 

(23.7%) and 2012 (23.3%).

• Trends in induction rates 

vary by gestational age, with 

rates for most gestational age 

groups declining since 2010. 

Induction rates for births at 36, 

37, and 38 weeks have declined 

since 2006, with the largest 

decrease at 38 weeks.

• From 2006 through 2012, 

induction rates at 38 weeks 

of gestation declined for all 

maternal age groups under 40 

and for each of the largest race 

and Hispanic origin groups.

• Induction rates at 38 weeks 

declined for 36 states and the 

District of Columbia (DC) 

from 2006 through 2012, with 

declines ranging from 5% to 

48%; rates for 31 states and DC 

declined at least 10%.

During the 1980s, 1990s, and through 2006, the length of pregnancies in 

the United States shortened (1). From 1981 through 2006, the proportion of 

infants born at less than 39 completed weeks of gestation increased nearly 

60%, while births at 39 weeks or more declined more than 20%. This shift 

in the gestational age distribution has been associated with greater use of 

cesarean delivery and induction of labor prior to full term (2–4). In more 

recent years, however, the trend towards shorter gestational ages has partially 

reversed. Since 2006, births delivered at less than 39 weeks have declined 

(down 12%), and births at 39 weeks or more have increased (up 9%) (1). This 

report explores trends in induction of labor for singleton births by gestational 

age, maternal age, race and Hispanic origin, and state for 2006–2012.

Keywords: race • Hispanic origin • maternal age

After increasing nearly every year since 1990, the induction 

of labor rate for singleton births declined in 2011 and 2012.

0

5

10

15

20

25

30

35

40

Postterm

Late term

Full term

Early term

Late preterm

Early preterm

All gestational

ages

2002 2004 2006 2008 2010 2012

Year

1990 1992 1994 1996 1998 2000

Figure 1. Induction of labor, by gestational age: United States, 1990–2012

NOTES: Singletons only. Early preterm is less than 34 weeks of gestation; late preterm is 34–36 weeks; early term is 37–38 weeks; 

full term is 39–40 weeks; late term is 41 weeks; postterm is 42 weeks or more. Access data table for Figure 1 at: 

http://www.cdc.gov/nchs/data/databriefs/db155_table.pdf#1.

SOURCE: CDC/NCHS, National Vital Statistics System. Percent
NCHS Data Brief ■ No. 155 ■ June 2014

■  2  ■

The rate of induction of labor more than doubled from 1990 through 2010, from 9.6% to 23.8% 

(Figure 1). Induction rates were at least twice as high in 2010 as in 1990 for all gestational age 

groups except postterm births, which rose 90%.

The overall induction rate declined slightly in 2011, to 23.7% (from 23.8% in 2010), and then 

declined again in 2012, to 23.3%.

There has been some variation in the year in which the decline in rates of labor induction began. 

Induction rates for late preterm and early-term births declined for the first time in 2007 and have 

done so nearly every year since. From 2006 through 2012, induction rates declined 4% for late 

preterm births (17.3% to 16.6%) and 12% for early-term births (21.0% to 18.4%). In contrast, 

rates for early preterm, and full-, late-, and postterm births were unchanged from 2010 to 2011, 

but declined in 2012 (1% to 3%).

From 2006 through 2012, induction rates declined at each gestational week 

35–38, with the greatest decline at 38 weeks.

Different patterns emerged in induction rate trends from 2006 through 2012 for late preterm 

and early-term births (Figure 2). The largest changes occurred among early-term births, with 

induction rates declining at both 37 (down 6%) and 38 (down 16%) weeks.

0

12

14

16

18

20

22

24 2006 2007 2008 2009 2010 2011 2012

Percent

Figure 2. Induction of labor at each gestational week 34–38: United States, 2006–2012

NOTES: Singletons only. Thirty-four, 35, and 36 weeks are late preterm; 37 and 38 weeks are early term. Access data table for Figure 2 at: http://www.cdc.gov/

nchs/data/databriefs/db155_table.pdf#2.

SOURCE: CDC/NCHS, National Vital Statistics System. 

Late preterm Early term

Gestational age (completed weeks)

34 35 36 37 38
NCHS Data Brief ■ No. 155 ■ June 2014

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Among late preterm births, induction rates at 35 weeks declined 3%. At 36 weeks, the rate was 

down 7%. In contrast, induction rates at 34 weeks fluctuated from 15.9% (2006) to 16.6% (2010 

and 2012), increasing 4% during the study period. 

For each week 36–38, most of the decline has occurred since 2008.

From 2006 through 2012, induction rates at 38 weeks of gestation declined 

for all maternal age groups under 40.

Trends in induction rates at each week 35–38 varied by maternal age from 2006 through 2012 

(Figure 3). At 38 weeks, induction rates declined for all maternal age groups under 40, dropping 

13%–19% for women in their 20s and 30s.

Under 20 20–24 25–29 30–34 35–39 40 or more

Gestational age (completed weeks)

Figure 3. Change in induction rates at each gestational week 35–38, by age of mother: United States, 2006 and 2012

* Change not statistically significant at 0.05 level.

NOTES: Singletons only. Thirty-five and 36 weeks are late preterm; 37 and 38 weeks are early term. Access data table for Figure 3 at: http://www.cdc.gov/ nchs/

data/databriefs/db155_table.pdf#3.

SOURCE: CDC/NCHS, National Vital Statistics System.

-20

-15

-10

-5

0

5

10

15

38 weeks

35 weeks 36 weeks 37 weeks

Percent

*

*

*

*

* *

At 36 and 37 weeks, induction rates also declined among women in their 20s and 30s, with rates 

for women aged 25–29 dropping 9%–10% from 2006 through 2012.

Induction rates at 35 weeks declined for women aged 25–29 (4%) and 35–39 (7%) from 2006 

through 2012.

Patterns varied for the youngest and oldest moms. Whereas induction rates at 38 weeks declined 

for women under 20 from 2006 through 2012, rates at 35, 36, and 37 weeks increased 5%–10% 

for this age group. Induction rates for women aged 40 and over were essentially unchanged for all 

weeks 35–38 during this time.
NCHS Data Brief ■ No. 155 ■ June 2014

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Changes in induction rates at 35–38 weeks varied by race and Hispanic 

origin.

The largest changes for all groups from 2006 through 2012 were at 38 weeks (Figure 4). 

Induction rates were down for all three race and ethnicity groups: non-Hispanic white (down 

19%), non-Hispanic black (down 3%), and Hispanic (down 7%). For non-Hispanic white women, 

the induction rate at 38 weeks dropped from 25.9% to 21.1%.

-20

-15

-10

-5

0

5

10 Non-Hispanic white Non-Hispanic black Hispanic

35 weeks 36 weeks 37 weeks

38 weeks

* *

* *

Gestational age (completed weeks)

* Change not statistically significant at 0.05 level.

NOTES: Singletons only. Thirty-five and 36 weeks are late preterm; 37 and 38 weeks are early term. Access data table for Figure 4 at: http://www.cdc.gov/nchs/

data/databriefs/db155_table.pdf#4.

SOURCE: CDC/NCHS, National Vital Statistics System. Percent

Figure 4. Change in induction rates at each gestational week 35–38, by race and Hispanic origin: United States, 2006 

and 2012

Changes at weeks 35–37 were less consistent by race and Hispanic origin. Rates for nonHispanic white women decreased 6%–11% for all three gestational weeks. In contrast, rates for 

non-Hispanic black women increased at least 5% at 35 and 37 weeks and were unchanged at 36 

weeks. Rates for Hispanic women were unchanged at 35, 36, and 37 weeks.
NCHS Data Brief ■ No. 155 ■ June 2014

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From 2006 through 2012, induction rates at 38 weeks declined in nearly 

three-quarters of all states.

The largest declines in labor induction for the nation occurred at 38 weeks of gestation 

(Figure 5). Declines in labor induction occurred for almost 3 out of 4 states over the study period. 

For 36 states and the District of Columbia (DC), induction rates at 38 weeks were lower in 2012 

than in 2006. Declines ranged from 5% in Maryland to 48% in Utah. Rates declined at least 10% 

in 31 states and DC; rates in 5 states dropped at least 30% during this time.

Rates at 38 weeks increased for Alaska (33%), New York (11%), and North Carolina (9%) from 

2006 through 2012; rates for the remaining 11 states were unchanged.

* Change not statistically significant at 0.05 level.

NOTES: Singletons only. Thirty-eight weeks is early term. Access data table for Figure 5 at: http://www.cdc.gov/nchs/data/databriefs/db155_table.pdf#5.

SOURCE: CDC/NCHS, National Vital Statistics System.

Figure 5. Percent change in induction of labor rates at 38 weeks of gestation, by state: United States, 2006 and 2012

CA

AK

HI

10%–19% decrease

20%–29% decrease

30% or more decrease

ID

WA

OR

NV

AZ

ND

SD

NE

TX

KS MO

IA

MN

IL IN

MS

FL

OH

MI

PA

MD

DE

NJ

CT RI

MA

ME

VT

NH

MT

WY

UT

CO

NM

WI

DC

NY

SC

NC

GA

VA

AL

KY

WV

TN

OK AR

LA

1%–9% decrease

No change*

Increase
NCHS Data Brief ■ No. 155 ■ June 2014

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Summary

Following nearly 2 decades of steady increases during which the rate of induction of labor nearly 

doubled, the use of medical or surgical means to stimulate labor before spontaneous labor fell 

slightly in 2011, and again in 2012. Induction rates were down for all gestational age categories 

from 2010 through 2012. The onset of the decline varied by gestational age, with rates for 35–38 

weeks beginning to trend earlier than rates for other gestational ages.

Declines in induction rates at 35–38 weeks were observed for all maternal age groups 20–39, with 

the largest declines by gestational age reported at 38 weeks. Changes in induced labor for weeks 

35–37 by race and Hispanic origin were limited to non-Hispanic white women; however, rates 

at 38 weeks declined among each of the race and Hispanic origin groups studied, with declines 

ranging from 3% to 19%. Rates of induction of labor at 38 weeks also fell for most states (36 

states and DC) from 2006 through 2012, with declines by at least one-fifth reported for 16 states 

and DC. An earlier report that examined changes in cesarean delivery rates by gestational age for 

2009–2011 found similar declines in cesarean delivery at 38 weeks (5).

The decline in induction rates at 35–38 weeks from 2006 is concurrent with the decline in 

overall rates of late preterm (34–36 weeks) and early-term (37–38 weeks) births (1). Changes 

in induction of labor, particularly at 35–38 weeks, may be associated with changes in obstetric 

practice, as research has demonstrated greater risks of morbidity and mortality among infants 

delivered during these weeks compared with those delivered later in pregnancy (3,6,7).

Definitions

Induction of labor: Initiation of uterine contractions by medical and/or surgical means for the 

purpose of delivery before the spontaneous onset of labor (i.e., before labor has begun).

Induction rate: Births with induction of labor per 100 births.

Singleton birth: Individual live birth in a singleton (one fetus) pregnancy.

Singleton induction rate: Number of labor inductions for singleton births per 100 singleton births.

Gestational age categories: 

Early preterm: Births prior to 34 completed weeks of gestation.

Late preterm: Births at 34–36 completed weeks of gestation.

Early term: Births at 37–38 completed weeks of gestation.

Full term: Births at 39–40 completed weeks of gestation.

Late term: Births at 41 completed weeks of gestation.

Postterm: Births at 42 or more completed weeks of gestation.
NCHS Data Brief ■ No. 155 ■ June 2014

■  7  ■

Data source and methods

This report is based on 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. Final data 

may also be accessed from the interactive data access tool, VitalStats (8).

This data brief focuses on births in singleton deliveries, which make up the bulk of all newborns 

(96.6% in 2012). Births in multiple deliveries are excluded because of differences in the way 

labor and delivery is managed for multiple gestation pregnancies.

The primary measure used to determine gestational age is the interval between the first day of 

the mother’s last normal menstrual period (LMP) and the date of birth. The clinical or obstetric 

estimate of gestation is substituted where the LMP is missing or inconsistent with birthweight (9).

References to rate increases or decreases indicate statistically significant differences. 

Computations exclude records with missing data.

Levels of missing data for induction of labor have been consistently low during the study period, 

ranging only from 0.2% to 0.6% (10). It is important to note, however, that induction of labor is 

underreported on the birth certificate. According to a validity study in two states, the sensitivity 

of the induction of labor question was substantial (86.0% chance that what was captured on the 

birth certificate was actually in the medical record) for one state and low (45.9%) for the other. 

For more details, see “Assessing the Quality of Medical and Health Data From the 2003 Birth 

Certificate Revision: Results From Two States” (11).

About the authors

Michelle J.K. Osterman and Joyce A. Martin are with CDC’s National Center for Health 

Statistics, Division of Vital Statistics, Reproductive Statistics Branch.

References

1. Martin JA, Hamilton BE, Osterman MJK, et al. Births: Final data for 2012. National vital 

statistics reports; vol 62 no 9. Hyattsville, MD: National Center for Health Statistics. 2013.

2. MacDorman MF, Declercq E, Zhang J. Obstetrical intervention and the singleton preterm 

birth rate in the United States from 1991–2006. Am J Public Health 100(11):2241–7. 2010.

3. Engle WA, Kominiarek MA. Late preterm infants, early term infants, and timing of elective 

deliveries. Clin Perinatol 35(2):325–41. 2008.

4. Ehrenthal DB, Hoffman MK, Jiang X, Ostrum G. Neonatal outcomes after implementation of 

guidelines limiting elective delivery before 39 weeks of gestation. Obstet Gynecol 118(5):1047–

55. 2011.

5. Osterman MJK, Martin JA. Changes in cesarean delivery rates by gestational age: 

United States, 1996–2011. NCHS data brief, no 124. Hyattsville, MD: National Center for Health 

Statistics. 2013.
NCHS Data Brief ■ No. 155 ■ June 2014

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6. Ashton DM. Elective delivery at less than 39 weeks. Curr Opin Obstet 

Gynecol 22(6):506–10. 2010.

7. American College of Obstetricians and Gynecologists. ACOG committee 

opinion no. 561: Nonmedically indicated early-term deliveries. Obstet 

Gynecol 121(4):911–5. 2013.

8. NCHS. VitalStats. Available from: http://www.cdc.gov/nchs/vitalstats.

htm.

9. NCHS. User guide to the 2012 natality public use file. Annual product 

2013. Available from: ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_

Documentation/DVS/natality/UserGuide2012.pdf. 

10. NCHS. User guide to the 2006–2011 natality public use files. Annual 

products 2013. Available from: http://www.cdc.gov/nchs/data_access/

VitalStatsOnline.htm. 

11. Martin JA, Wilson EC, Osterman MJK, et al. Assessing the quality of 

medical and health data from the 2003 birth certificate revision: Results from 

two states. National vital statistics reports; vol 62 no 2. Hyattsville, MD: 

National Center for Health Statistics. 2013.

Suggested citation

Osterman MJK, Martin JA. Recent declines 

in induction of labor by gestational age. 

NCHS data brief, no 155. Hyattsville, MD: 

National Center for Health Statistics. 2014.

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

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