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America's Children: Key National Indicators of Well-Being, 2009

Preterm Birth and Low Birthweight

Infants born preterm (less than 37 completed weeks of gestation) or with low birthweight (less than 2,500 grams or 5 lbs. 8 oz.) are at higher risk of early death and long-term health and developmental issues than infants born later in pregnancy or at higher birthweights.9,114,115 Many, but not all, preterm infants are also low birthweight, and vice versa. In 2006, infants born preterm accounted for two-thirds of all low birthweight infants, and over 40 percent of preterm births were low birthweight.6 Preterm infants born at less than 34 weeks (very and moderately preterm) are at high risk for poor outcomes, including chronic health conditions, long-term disability, and death. The majority of preterm births are infants born at 34–36 weeks (late preterm). Late preterm infants are at lower risk of poor outcomes than infants born earlier but are at higher risk than infants delivered at term or later.9 Disorders related to preterm birth and low birthweight are the second leading cause of infant death in the United States.9

Indicator HEALTH1.A: Percentage of infants born preterm and percentage of infants born with low birthweight, 1990–2007
Percentage of infants born preterm and percentage of infants born with low birthweight, 1990–2007

NOTE: Late preterm infants are born at 34–36 weeks of gestation; very and moderately preterm infants are born at less than 34 weeks gestation. Moderately low birthweight infants weigh 1,500–2,499 grams at birth; very low birthweight infants weigh less than 1,500 grams at birth.

SOURCE: National Center for Health Statistics, National Vital Statistics System.

  • After several decades of steady increases, the percentage of infants born preterm and the percentage born with low birthweight declined slightly in 2007. The percentage of infants born preterm was 12.7 percent in 2007, down from 12.8 percent in 2006; most of the decline was among late preterm infants (from 9.1 percent in 2006 to 9.0 percent in 2007). The percentage of infants born with low birthweight declined to 8.2 percent in 2007 from 8.3 percent in 2006; all of the decline was among moderately low birthweight infants.
  • From 1990 to 2006, the percentage of preterm births rose from 10.6 percent to 12.8 percent. The increase in late preterm births (from 7.3 to 9.1 percent) accounted for most of this increase. The percentage of births that were very and moderately preterm changed little in recent years (3.6 percent in 2007).
  • The percentage of low birthweight infants rose from 7.0 percent of all births in 1990 to 8.3 percent in 2006. In 2006 and 2007, 1.5 percent of infants were very low birthweight, up from 1.3 percent in 1990. The percentage of moderately low birthweight infants rose from 5.7 percent in 1990 to 6.8 percent in 2006, but declined slightly to 6.7 percent in 2007.
  • The increasing multiple birth rate was a contributing factor to the rise in preterm birth and low birthweight between 1990 and 2006. However, both the percentage of preterm births and low birthweight infants rose substantially among singleton births as well.6

Indicator HEALTH1.B: Percentage of infants born with low birthweight by race and Hispanic origin of mother, 1990, 2006, and 2007
Percentage of infants born with low birthweight by race and Hispanic origin of mother, 1990, 2006, and 2007

NOTE: Data for 2007 are preliminary. Race refers to mother's race. The 1977 OMB Standards for Data on Race and Ethnicity were used to classify persons into one of the following four racial groups: White, Black, American Indian or Alaskan Native, or Asian or Pacific Islander. Although state reporting of birth certificate data is transitioning to comply with the 1997 OMB standard for race and ethnic statistics, 2006 and 2007 data from states reporting multiple races were bridged to the single-race categories of the 1977 OMB standards for comparability with other states. Data on race and Hispanic origin are collected and reported separately. Persons of Hispanic origin may be of any race.

SOURCE: National Center for Health Statistics, National Vital Statistics System.

  • The percentage of Black, non-Hispanic infants born with low birthweight was higher than that of other racial or ethnic groups. The Black, non-Hispanic percentage declined to a low of 13.1 percent in 1996 and 1997, rose to 14.0 percent in 2006, and declined to 13.8 percent in 2007. The percentage of low birthweight infants rose among White, non-Hispanic infants, from 5.6 percent in 1990 to 7.3 percent in 2006, but declined slightly to 7.2 percent in 2007. Between 1990 and 2006, low birthweight percentages increased for American Indian or Alaskan Native infants (6.1 to 7.5 percent) and Asian or Pacific Islander infants (6.5 to 8.1 percent); the percentages for both groups, however, were unchanged between 2006 and 2007. Among Hispanic infants, the percentage of low birthweight infants rose between 1990 and 2006 (6.1 to 7.0 percent) and declined slightly for 2007 (6.9 percent).
  • In 2007, Black, non-Hispanic infants were also more likely to be born preterm (18 percent) than White, non-Hispanic (11 percent) and Hispanic (12 percent) infants.
  • The percentage of Black, non-Hispanic infants born preterm declined from 19.0 percent in 1991 to 17.4 percent in 2000, rose to 18.5 percent in 2006, and declined slightly in 2007 (18.3 percent). From 1990 to 2006, the percentage of preterm births increased steadily for White, non-Hispanic infants (8.5 to 11.7 percent), then declined slightly in 2007 (11.5 percent). The percentage of preterm Hispanic infants increased from 11.0 to 12.3 percent between 1990 and 2007.

table icon HEALTH1.A HTML Table, HEALTH1.B HTML Table

6 Martin, J.A., Hamilton, B.E., Sutton, P.D., Ventura, S.J., Menacker, F.J. Kirmeyer, S., and Mathews, TJ. (2009). Births: Final data for 2006. National Vital Statistics Reports 57(7). Hyattsville, MD: National Center for Health Statistics.

9 Mathews, T.J., and MacDorman, M.F. (2008). Infant mortality statistics from the 2005 period linked birth/infant death data set. National Vital Statistics Reports, 57(2). Hyattsville, MD: National Center for Health Statistics.

114 Institute of Medicine, Committee on Understanding Premature Birth and Assuring Healthy Outcomes and Board on Health Sciences Policy. (2005). Preterm birth: Causes, consequences, and prevention. R.E. Behrman and A.S. Butler. (Eds). Washington, DC: The National Academies Press.

115 Hack, M., Taylor, H.G., Droter, D., Schluchter, M., Cartar, L., Andreias, L., Wilson-Costello, D., and Klein, N. (2005). Chronic conditions, functional limitations, and special health care needs of school-aged children born with extremely low birthweight in the 1990s. Journal of the American Medical Association 294: 318–325.