Bacterial vaginosis in pregnancy and efficacy of short-course oral metronidazole treatment: A randomized controlled trial

Objective: To characterize the natural history of bacterial vaginosis in pregnancy and to assess the efficacy of short courses of oral metronidazole therapy for long-term suppression of bacterial vaginosis flora. Methods: This was a randomized, double-blind, placebo-controlled study of two 2-day courses of metronidazole (400 mg twice daily) in pregnant women with bacterial vaginosis (by Gram stain) and/or heavy growth of Gardnerclla vaginalis. The first course was given at 24 weeks’ gestation and a second course at 29 weeks if the follow-up vaginal swab grew G vaginalis. Follow-up swabs were performed at 28, 32, and 36 weeks’ gestation. Results: On the basis of their G vaginalis colonization, 196 women were enrolled, and 137 were evaluable for efficacy, including 66 with bacterial vaginosis. The microbial ecology of bacterial vaginosis in 36 women in the placebo group was relatively stable, with 72% persistence at 28 weeks and 57% at 32 weeks’ gestation. Metronidazole effectively suppressed bacterial vaginosis for 4 weeks after the first course in 76%, compared with 28% in the placebo group, and had a cumulative efficacy of 87% compared to 44% 4 weeks after the second course (odds ratio 0.12, 95% confidence interval 0.03–0.5). Conclusions: The microbial ecology of bacterial vaginosis in pregnant women is relatively stable. Long-term suppression of bacterial vaginosis flora for 2–3 months can be achieved by short courses of metronidazole therapy in 87% of women in mid-pregnancy. Because bacterial vaginosis has been associated with an increased risk of preterm labor, these findings provide the foundation for an intervention study of women with bacterial vaginosis in pregnancy.