Objective: To examine black-white differences in preterm delivery in a healthy population who had unrestricted access to prenatal care.
Methods: We conducted a retrospective cohort study of 842 black and 1026 white enlisted servicewomen who delivered a singleton infant of 20 or more weeks' gestation from July 1, 1987 through September 30, 1990 at four Army Medical Centers in the United States. Data were collected by reviewing maternal and newborn records. We used logistic and proportional hazards regression models to analyze outcomes defined by length of gestation, cause of preterm delivery, and jointly by length and cause.
Results: Black enlisted women had a cumulative probability of preterm delivery (13.5%) that was higher than that for white enlisted women (10.5%) (hazard ratio 1.31, 95% confidence interval [CI] 1.002-1.70). However, the ratio of black-to-white hazards was not uniform. Black-white differences were small and nonsignificant from 33-36 weeks' gestation, when most preterm deliveries occur. The differences were also small and nonsignificant for deliveries related to spontaneous rupture of membranes or idiopathic preterm labor, the most common causes of preterm delivery. The black-to-white hazard ratios were greatest for all deliveries before 33 weeks' gestation and for medically indicated preterm deliveries.
Conclusions: Efforts to reduce black-white differences in preterm delivery must go beyond providing prenatal care and eliminating recreational drug use. Future studies should consider black-white differences in environments during the mother's own development and in psychosocial and physical stresses during pregnancy.