Preterm birth, which occurs in 11 percent of all pregnancies, is responsible for the majority of neonatal deaths and nearly one half of all cases of congenital neurologic disability, including cerebral palsy.1Although all births before 37 weeks of gestation are considered premature, births before 32 weeks' gestation (2 percent of all births) account for most neonatal deaths and disorders.2 State and national vital statistics indicate that the incidence of preterm birth has risen over the past 15 years (Figure 1), and it remains twice as high among black women as among white women.35 Preterm birth is commonly categorized . . .