NCHS Data Brief ■ No. 39 ■ May 2010

u.s. department of health and human services

centers for disease control and prevention

national center for health statistics

Are Preterm Births on the Decline in the United States?

Recent Data From the National Vital Statistics System

Joyce a. martin, m.p.h.; michelle J.K. osterman, m.h.s.; and paul d. sutton, ph.d.

Key findings

•	 Following a long period of 

fairly steady increase, the U.S. 

preterm birth rate declined 

for the second straight year 

in 2008 to 12.3 percent, from 

12.8 percent in 2006.

•	 	This	marks	the	first	2-year	

decline in the preterm birth 

rate in nearly three decades.

•	 Preterm birth rates declined 

from 2006 to 2008 for mothers 

of all age groups under age 40, 

for the three largest race and 

Hispanic origin groups and for 

most U.S. states.

•	 The percentage of preterm 

births was down for all types 

of deliveries from 2006 to 

2008, for cesareans and for 

induced and noninduced 

vaginal deliveries. 

The U.S. preterm birth rate (less than 37 weeks of gestation) rose by more 

than	one-third	from	the	early	1980s	through	2006	(1).	This	rise	has	been	a	

cause	of	great	concern	(2,3).	Preterm	infants	are	at	increased	risk	of	life-long	

disability and early death compared with infants born later in pregnancy (2,4). 

Many reasons, such as changes in maternal demographics and increases in 

multiple births, have been suggested for the growth in preterm births (5). 

Another factor cited is the heightened use of obstetric interventions such 

as induction of labor and cesarean delivery earlier in pregnancy (5,6,7). 

Although it is not possible to know whether an infant would be born preterm 

if labor was not induced or delivered by cesarean, studies suggest that 

increased use of these procedures before 37 completed weeks of gestation 

may	have	influenced	the	upswing	in	preterm	birth	rates	(6,7).	

Preliminary	2007	and	2008	birth	certificate	data	reveal	a	shift	in	the	long	

upward	trend	in	preterm	births	(8,9).	This	report	describes	this	change.

Keywords: preterm, late preterm, state-specific preterm birth rates 

The U.S. preterm rate declines for the second straight 

year―the first 2-year decline in nearly three decades.

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NCHS Data Brief ■ No. 39 ■ May 2010

■  2  ■

•	 The U.S. preterm birth rate declined for the second straight year in 2008, to 12.3 percent of 

all births, down 3 percent from 2007 (12.7 percent) and 4 percent from 2006 (12.8) (Figure

1). 

•	 The	preterm	rate	had	been	generally	climbing	since	1981,	rising	13	percent	from	1981	(the	

earliest	year	for	which	comparable	data	are	available)	to	1990	and	more	than	20	percent	for	

the	more	recent	period,	1990	to	2006	(1).

•	 The percentage of infants born late preterm (34 to 36 weeks of gestation) declined 3 percent, 

from	9.1	percent	in	2006	to	8.8	percent	in	2008;	the	late	preterm	birth	rate	had	risen	25	

percent	between	1990	(7.3	percent)	and	2006.	Although	at	less	risk	than	infants	born	before	

34	weeks,	late	preterm	infants	are	more	likely	to	experience	long-term	neurodevelopmental	

problems	and	to	die	within	the	first	year	of	life	than	infants	born	at	term	(2,4).

•	 The percentage of newborns delivered early preterm (less than 34 weeks of gestation) was 

also down in 2008, to 3.6 percent, compared with 3.7 percent in 2006. This level had risen 

from	3.3	percent	in	1990.	Infants	delivered	early	preterm	are	much	more	likely	to	suffer	

long-term	disability	and	early	death	than	those	born	after	34	weeks	(2,4).

Preterm births are down for women of all age groups under age 40.

•	 Preterm rates were lower for births to women of all age groups under age 40 years in 2008 

compared with 2006 (Figure 2). Rates declined by 3 to 5 percent among births to women 

under	age	35	years,	and	by	2	percent	for	women	35–39	years.	Changes	for	age	groups	40–44	

and	45–54	years	were	not	statistically	significant.	

•	 From	1990	to	2006,	preterm	rates	had	been	on	the	rise	among	women	of	all	age	groups.

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NCHS Data Brief ■ No. 39 ■ May 2010

■  3  ■

From 2006 to 2008, preterm birth rates dropped 5 percent among nonHispanic white and non-Hispanic black infants. 

•	 The	2008	preterm	rate	for	non-Hispanic	white	infants	was	11.1	percent,	3	percent	lower	than	

2007 (11.5 percent) and 5 percent lower than 2006 (11.7 percent) (Figure 3). Preterm births 

among	non-Hispanic	white	infants	had	climbed	38	percent	from	1990	to	2006	(from	8.5	

percent). 

•	 The	preterm	birth	rate	for	non-Hispanic	black	newborns	declined	to	17.5	percent	in	2008,	

down 5 percent from 2006 (18.5 percent), and among the lowest levels ever reported (rates 

of	17.4	and	17.5	percent	were	previously	reported)	(Figure	3).	Preterm	rates	for	nonHispanic	black	infants	had	trended	downward	during	much	of	the	1990s,	but	rose	between	

2000 and 2006. 

•	 The preterm birth rate for Hispanic infants declined from 12.3 to 12.1 percent from 2007 to 

2008. This reduction follows a small increase between 2006 and 2007. Preterm rates among 

Hispanic	infants	fluctuated	from	1990	to	2007,	but	rose	by	a	total	of	12	percent	over	this	

period	(from	11.0	percent	in	1990).

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NCHS Data Brief ■ No. 39 ■ May 2010

■  4  ■

Preterm birth rates decline in most U.S. states.

•	 Since	2006	when	the	national	rate	peaked,	preterm	birth	rates	have	declined	significantly	in	

35 states (Figure 4). Only one state, Hawaii, reported an increase in preterm births. 

•	 Before	the	recent	downward	trend,	rates	had	increased	significantly	in	all	50	states	from	

1990	to	2006.	The	only	exception	to	this	trend	was	the	District	of	Columbia,	for	which	

the	rate	declined.	(Preliminary	2008	preterm	and	late	preterm	state-specific	birth	rates	are	

available at: http://www.cdc.gov/nchs/data/nvsr/nvsr58/nvsr58_16_tables.pdf#d.)

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NCHS Data Brief ■ No. 39 ■ May 2010

■  5  ■

Preterm births are less likely among all types of deliveries.

•	 Preliminary 2008 data reveal that the percentage of all cesarean births that were preterm 

declined 4 percent from 2006 to 2008, from 17.8 to 17.1 percent. 

•	 The percentage of induced vaginal births born preterm also decreased over this period, from 

7.7 to 7.2 percent, as did the percentage of noninduced vaginal births, down from 11.6 to 

11.1 percent (Figure 5). 

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NCHS Data Brief ■ No. 39 ■ May 2010

■  6  ■

Summary

Following a long period of fairly steady increase, the U.S. preterm birth rate declined in 2007 

(from	12.8	to	12.7	percent),	and	then	again	in	2008	(to	12.3	percent),	marking	the	first	2-year	

downturn	in	this	rate	in	nearly	three	decades.	Declines	in	preterm	birth	rates	from	2006	to	2008	

were observed for mothers of all age groups under age 40, for the three largest race and Hispanic 

origin groups, for the majority of all states, and for all types of deliveries. 

The reduction in the overall preterm birth rate is not explained by changes in the proportions of 

multiple births (multiples are at much greater risk than singletons of preterm delivery). Preterm 

rates among singleton births declined by a similar amount as for all births over this period (from 

11.1 to 10.6 percent.) 

Previous research has suggested that increases in preterm induction of labor and cesarean 

delivery	contributed	to	the	rise	in	the	overall	preterm	birth	rate	(6,7).	Decreases	in	the	use	of	

these	procedures	before	37	weeks	could	also	potentially	reduce	this	rate.	This	report	finds	that	

the decline in the overall preterm rate from 2006 to 2008 was related to declines in all types of 

delivery, that is, in preterm cesarean and induced and noninduced vaginal births.

Although	lower	in	2008,	the	U.S.	preterm	birth	rate	remains	higher	than	in	any	year	from	1981	

to 2002, with large differences still evident by race and Hispanic origin. Further research is 

necessary to explain the factors behind the current downturn and to develop approaches to help 

ensure its continued decline.

Definitions

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

per 100 total births.

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

per 100 total births.

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

gestation per 100 total births.

Multiple births: Births in twin and triplet and higher order multiple deliveries.

Cesarean: Extraction of the infant, placenta, and membranes through an incision in the maternal 

abdominal and uterine walls.

Vaginal:	Delivery	of	the	fetus	through	the	vagina.

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

of delivery before the spontaneous onset of labor (i.e., before labor has begun).
NCHS Data Brief ■ No. 39 ■ May 2010

■  7  ■

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	for	all	births	occurring	in	the	United	States.	

The	natality	files	include	information	on	a	wide	range	of	maternal	and	infant	demographic	and	

health characteristics for babies born in the United States. Final data may also be accessed from 

the interactive data access tool, VitalStats.

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 (1). 

About the authors

Joyce	A.	Martin,	Michelle	J.K.	Osterman,	and	Paul	D.	Sutton	are	with	the	Centers	for	Disease	

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

Reproductive Statistics Branch. Brady Hamilton, Sharon Kirmeyer, and T.J. Mathews, also with 

the Reproductive Statistics Branch, provided helpful comments on this report.

References

1. 	Martin	JA,	Hamilton	BE,	Sutton	PD,	et	al.	Births:	Final	data	for	2006.	National	vital	

statistics	reports;	vol	57,	no	7.	Hyattsville,	MD:	National	Center	for	Health	Statistics.	2008.

2. Behrman	RE,	Butler	AS,	ed.	Preterm	birth:	causes,	consequences,	and	prevention.	Committee	

on understanding premature birth and assuring healthy outcomes, Board on Health Sciences 

Policy.	Institute	of	Medicine.	Nat’l	Academies	Press.	2005.

3. March	of	Dimes.	Prematurity	Campaign	2008	Progress	Report.	2009.	Available	from:	http://

www.marchofdimes.com/files/PrematurityCampaign2008AccompHR_sm.pdf.

4. 	Mathews	TJ,	MacDorman	MF.	Infant	mortality	statistics	from	the	2006	period	linked	birth/

infant	death	data	set.	National	vital	statistics	reports;	vol	58,	no	17.	Hyattsville,	MD:	National	

Center	for	Health	Statistics.	2010.

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

deliveries.	Clinics	in	perinatol	35(2):325–41.	2008.

6. Fuchs K, Wapner R. Elective cesarean section and induction and their impact on late preterm 

births.	Clinics	in	perinatol	33(4):793–800.	2006.

7. 	Bettegowda	VR,	Dias	T,	Davidoff	MJ,	et	al.	The	relationship	between	cesarean	delivery	and	

gestational	age	among	U.S.	singleton	births.	Clinics	in	perinatol	35(2):309–23.	2008.

8. Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2007. National vital 

statistics	reports;	vol	57	no	12.	Hyattsville,	MD:	National	Center	for	Health	Statistics.	Online	

only	release.	March	18,	2009.	

9.	 Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2008. National vital 

statistics	reports;	vol	58	no	16.	Hyattsville,	MD:	National	Center	for	Health	Statistics.	Online	

only release. April 6, 2010.
NCHS Data Brief ■ No. 39 ■ May 2010

ISSN 1941–4927 (Print ed.) 

ISSN 1941–4935 (Online ed.) 

CS212603

T36574 (05/2010) 

DHHS	Publication	No.	(PHS)	2010–1209