Racial and ethnic differences in preterm delivery among low-risk women

Preterm delivery is the leading cause of infant mortality in the United States. The risk of preterm delivery and the prevalence of factors associated with preterm delivery differ by racial and ethnic groups.

To examine racial and ethnic differences in preterm delivery among women without the common risk factors for preterm delivery.

We used data from the Pregnancy Risk Assessment Monitoring System (PRAMS) for singleton births occurring in selected US states between 1988 and 2002. PRAMS is a cross-sectional study of state residents who delivered a live birth within the state. We defined risk status using maternal age, education, marital status at delivery, parity, interpregnancy interval, tobacco or alcohol use, source and amount of income, and pre-pregnancy body mass index.

Only 9.6% (18,815) of women were low risk. Between 2.4% (Native Americans) and 12.4% (Asian-Pacific Islanders) were low risk. Low-risk women were 29.0% (95% CI: 23.0%, 34.0%) less likely to deliver preterm than non-low-risk women. Among low-risk women, African American women had more preterm births than White women (PR: 1.3, 95% CI: 1.0, 1.6), but only among multiparous women whose most recent prior birth was neither low birth weight nor preterm.

Traditional risk factors explain about half of the excess prevalence of preterm births among African Americans and explain all of the excess among other racial and ethnic groups. The remaining excess among African American appears to be due to risk factors among multiparous women that occur between pregnancies.