Preterm delivery and perinatal death among black and white infants in a Chicago-area perinatal registry.

Objective: To explore associations between race, preterm delivery, etiologic classification of preterm delivery, and perinatal mortality.
Methods: The study population consisted of 13,010 black and 19,007 white mother-infant pairs delivered at Chicago-area hospitals in 1988-1989 categorized as term or preterm births. Preterm births were further divided by severity and etiology. Black-white differences in perinatal mortality within groups were calculated and adjusted for birth weight and other potential confounding variables.
Results: Black women were nearly twice as likely as whites to experience preterm (before 37 weeks' gestation) and very preterm (before 32 weeks' gestation) delivery associated with premature rupture of membranes (PROM) or classified as idiopathic. Although black infants were also found to have twice the perinatal mortality risk of white infants (relative risk [RR] 2.1, 95% confidence interval [CI] 1.7-2.5), the overall preterm perinatal mortality rates did not differ between black and white women (RR 1.0, 95% CI 0.8-1.2). However, among preterm births, perinatal mortality was not uniform within categories of medical etiology. The mortality risk was the same for black and white infants born preterm following polyhydramnios or placental complications (RR 1.1, 95% CI 0.6-1.9), the same for black and white infants born preterm after labor induction (RR 1.1, 95% CI 0.6-1.9), and higher for black infants classified as idiopathic preterm deliveries (RR 1.6, 95% CI 1.1-2.3). In contrast, mortality rates tended to be lower for black infants born preterm following PROM-amnionitis (RR 0.8, 95% CI 0.5-1.2). The idiopathic disparity was explained by a differential birth weight distribution (adjusted RR 1.1, 95% CI 0.7-1.9); however, the apparent survival benefit among black infants born preterm following PROM increased even further after adjustment for birth weight (adjusted RR 0.4, 95% CI 0.2-0.7).
Conclusion: Black infants born preterm after PROM appear to have a survival advantage compared with their white counterparts, an effect not observed within other etiologic categories of preterm delivery.