Preterm singleton births--United States, 1989-1996.

Preterm birth (birth at <37 completed weeks of gestation) is the second leading cause of neonatal mortality in the United States. Preterm birthrates differ by race; in 1996, black infants were 1.8 times more likely than white infants to be preterm. From 1989 through 1996, the overall rate of preterm birth (per 1000 live-born infants) increased 4%, and the rate of multiple births (e.g., twins, triplets, or other higher-order births) increased 19%. Multiple births are associated with preterm birth; trends in preterm births independent of the influence of multiple births have not been fully explored. To characterize race- and ethnicity-specific trends in preterm birth independent of multiple births, data from U.S. birth certificates for 1989-1996 were analyzed for singleton births only. This report summarizes the results of this analysis and indicates that although singleton preterm birthrates are stable overall, substantial changes in rates occurred in some racial/ethnic subgroups.