CLINICAL AND ENVIRONMENTAL PREDICTORS OF PRETERM LABOR

Objective: To determine the magnitude of risk for preterm labor associ ated with specific clinical and environmental factors. Methods: Using a case-control design, 266 women with preterm labor and 512 controls w ere interviewed and their medical records reviewed. Crude and adjusted odds ratios were calculated for each risk factor. Population-attribut able risks were estimated. Results: Third-trimester bleeding, twin ges tation, and chorioamnionitis at presentation were strongly associated with preterm labor (odds ratios 11.2-48.3). A history of a prior prete rm delivery, vaginal bleeding in the first or second trimester, matern al diethylstilbestrol exposure, uterine anomalies, and urinary tract i nfection during pregnancy were associated to a lesser extent (odds rat ios 1.6-5.4), as were cigarette smoking and drug use (odds ratios 2.0 and 3.0). Cases who had preterm labor preceded by premature rupture of the membranes had a substantially higher risk of preterm labor if cho rioamnionitis, vaginal bleeding early in pregnancy, or urinary tract i nfection was present. By contrast, women who had intact membranes at t he onset of preterm labor carried higher risk when twin gestation, pla cental abruption, or uterine anomaly was present. The highest populati on-attributable risks for preterm labor were found in patients with a twin gestation or third-trimester bleeding. Conclusions: Programs to r educe the preterm delivery rate should consider the attributable risks for the factors they are intended to modify. The attributable risks w e obtained suggest that medical strategies to reduce the impact of the clinical variables, especially multiple gestation, and educational pr ograms to decrease smoking and drug use should reduce the preterm deli very rate.