Statespecific trends in preterm delivery: are rates really declining among non-Hispanic African Americans across the United States

Objectives: This study sought to examine state-specific trends in preterm delivery rates among non-Hispanic African Americans and to assess whether these rates are influenced by mis-classification of gestational age. Methods: The sample population consisted of singleton non-Hispanic White and non-Hispanic African–American infants born in 1991 and 2001 to U.S. resident mothers. For both time periods, state-specific and national preterm delivery rates were calculated for all infants, stratified by infant race/ethnicity. Next, birth-weight distribu-tions within strata of gestational age were studied to explore possible misclassifications of gestational age. Lastly, state-specific and national preterm delivery rates among infants who weighed less than 2,500 g were separately computed. Results: National analyses showed that the frequency of preterm delivery increased by 15.8 % among non-Hispanic Whites but de-clined by 10.3 % among non-Hispanic African Americans over the same period. For both subgroups, a bimodal distribution of birth weights was apparent among preterm births at 28– 31 weeks of gestation. The second peak with its cluster of normal-weight infants was more prominent among non-Hispanic African Americans in 1991 than in 2001. After excluding preterm infants who weighed 2,500 g or more, the national trends persisted. State-specifi