Group B Streptococcus and preterm premature rupture of membranes: A randomized, double-blind clinical trial of antepartum ampicillin

OBJECTIVE: Our purpose was to determine whether ampicillin prolongs the latency period after preterm premature rupture of membranes in patients colonized with group B Streptococcus. STUDY DESIGN: Sixty patients presenting at less than or equal to 35 weeks' gestation with preterm premature rupture of membranes were included in the study, Cervical, vaginal, and perianal cultures for group B Streptococcus were obtained. The participants then were randomized to receive either ampicillin or placebo intravenously for 24 hours and then orally until hospital discharge or delivery. All patients were treated without the use of tocolytic drugs, The chi(2) test, Fisher exact test, Student t test, and Wilcoxon signed-rank test were used for statistical analysis when appropriate. RESULTS: Fifteen patients had cultures positive for group B Streptococcus. Patients with cultures positive for group B Streptococcus who received ampicillin (n = 8) were more likely not to have been delivered of their infants 48 hours after preterm premature rupture of membranes than patients who received placebo (n = 7), a statistically significant difference (100% vs 43%; p = 0.01; relative risk, 2.3; 95% confidence interval 1.2 to 4.5). Seven days after preterm premature rupture of membranes, however, there was no significant difference in percentage of patients with cultures positive for group B Streptococcus who remained undelivered (63% vs 29%; p = 0.19; relative risk, 2.2; 95% confidence interval 0.7 to 7.1). Among patients with cultures negative for group B Streptococcus, there was a trend for patients who received ampicillin to remain undelivered 48 hours after preterm premature rupture of membranes compared with those who received placebo, but the difference was not statistically significant (87% vs 64%; p = 0.07; relative risk, 1.4; 95% confidence interval 1.0 to 1.9). There also was no difference in percentage of patients with cultures negative for group B Streptococcus who remained undelivered 7 days after preterm premature rupture of membranes (39% vs 27%; p = 0.40; relative risk, 1.4; 95% confidence interval 0.61 to 3.3). There were no differences between the treatment and placebo arms of the group B Streptococcus positive and negative cohorts in incidence of cesarean section, chorioamnionitis, postpartum endometritis, or neonatal infectious morbidity. CONCLUSION: Use of antibiotics increases the percentage of patients with cultures positive for group B Streptococcus who remain undelivered 48 hours after preterm premature rupture of membranes. Antibiotic therapy may provide a window of opportunity for maternal treatment with corticosteroids to decrease the risk for neonatal morbidity among these preterm gestations.