Preterm is defined as babies born alive before 37 weeks of pregnancy are completed. There are sub-categories of preterm birth, based on gestational age: extremely preterm (less than 28 weeks), very preterm (28 to 32 weeks), and moderate to late preterm (32 to 37 weeks).
This indicator, measured at the child level, can be calculated as the number of children born preterm (before 37 weeks of pregnancy) in the last year, divided by the total number of children born in the last year in a state/community.
The U.S. preterm birth rate rose by more than 20% 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% during this period. However, since then, the preterm birth rate has fallen by 10% and was at 11.4% in 2013. Black women have the highest rates of preterm births (16.3% in 2013), followed by American Indians (13.1%), Hispanics (11.3%), whites and Asian/Pacific Islanders (10.2%, each). The Healthy People 2020 goal is 11.4%.
- National Center for Health Statistics (NCHS) provides state-level data for 2013 by race, ethnicity, plurality, and birth weight. (Table I-8).
- Preliminary 2013 data for states (and some counties) are presented in the March of Dimes’ 2017 Premature Birth Report Card.
- State-level data on late preterm singleton birth rates for 1990–1991 and 2005–2006 are available in an NCHS Data Brief.
- Preterm births by state and in major cities for 1990–2012 are available from the Kids Count Data Center.
The underlying causes of preterm birth are poorly understood, although genetic, social, and environmental factors all likely play a role.1 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.2 Maternal depression during pregnancy may be another risk factor for preterm birth.3
Preterm birth can have significant implications for children’s intellectual development. Children born preterm tend to have lower intelligence and poorer school performance than children born full-term, and are at higher risk of intellectual disability, difficulty with complex language functions, and learning and behavioral problems. Quigley et al. (2012) find that the relationship between amount of time born prior to term and extent of decreased cognitive function is “quite linear, with the poorest performance seen in children who had been born before 32 weeks gestation, but seen even in children born late preterm (between 34 and 36 weeks).” Preterm birth is also associated with higher risk of health complications such as cerebral palsy, diabetes, high blood pressure, and heart disease.
- 1. Williamson, D.M., Abe, K., Bean, C., Ferré, C., et al. (2008). Current research in preterm birth. Journal of Women’s Health, 17(10).
- 2. March of Dimes (2012). What we know about prematurity. Retrieved from http://www.marchofdimes.com/mission/prematurity_indepth.html
- 3. 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.