RISK-FACTORS FOR PRETERM DELIVERY IN A HEALTHY COHORT

To examine whether risk factors differed among subgroups of preterm (< 37 weeks of gestation) deliveries, we studied a cohort of 1,825 enlist ed servicewomen who delivered from 1987 through 1990 at four U.S. Army medical centers. Preterm deliveries were classified by length of gest ation (<29 weeks, 29-32 weeks, 33-36 weeks) and clinical course [medic al indication, idiopathic preterm labor, or preterm rupture of membran es (PROM)]. We abstracted medical records for information on age, race , army rank, marital status, gravidity, parity, the baby's sex, matern al prepregnancy height and weight, gestation at entry to prenatal care , alcohol drinking and smoking, time since and outcome of preceding pr egnancy, surgery performed during pregnancy, anemia, and diagnoses of uterine abnormalities, sexually transmitted diseases, and urinary trac t infections. We used proportional hazards analysis to evaluate associ ations for each subgroup of preterm delivery. The relative odds associ ated with a history of preterm delivery in the preceding pregnancy ran ged from 3.1 for deliveries due to preterm labor or FROM to 6.2 for de liveries that occurred during 29-32 weeks; none of the other factors w as consistently associated across the subgroups of preterm delivery. T he paucity of associations is consistent with the conclusion of other investigators that most of the causes of preterm delivery are unknown.