Randomized investigation of antimicrobials for the prevention of preterm birth.

Objective: Occult amniotic fluid infection has emerged as a possible cause of many heretofore unexplained preterm births. We sought to determine whether antimicrobial therapy is effective in preventing preterm delivery.

Study Design: A double-blind, placebo-controlled, randomized trial was conducted to study the efficacy of ampicillin-sulbactam and amoxicillin-clavulanic acid in women hospitalized for preterm labor between 24 and 34 weeks' gestation. During this investigation no tocolytics or steroids were used.

Results: Thirty-nine women with preterm labor received antimicrobial therapy and 39 received placebos. The mean gestational ages at study entry were 29.8 +/- 0.4 weeks (SEM) and 30.6 +/- 0.3 weeks in the antimicrobial and placebo groups, respectively (not significant). Similarly, the mean gestational ages at delivery were 34.2 +/- 0.7 and 34.1 +/- 0.6 weeks, respectively (not significant). Other index values of pregnancy outcome, for example, birth weight, neonatal morbidity, and prenatal death, were not significantly improved by antimicrobial therapy given to the mother in preterm labor.

Conclusion: We find that antimicrobial therapy given to women in preterm labor is ineffective in the prevention of preterm birth.