Association between bacterial vaginosis or chlamydial infection and miscarriage before 16 weeks' gestation: prospective community based cohort study.

OBJECTIVES To assess whether bacterial vaginosis or chlamydial infection before 10 weeks' gestation is associated with miscarriage before 16 weeks. DESIGN Prospective cohort study. SETTING 32 general practices and five family planning clinics in south London. PARTICIPANTS 1216 pregnant women, mean age 31, presenting before 10 weeks' gestation. MAIN OUTCOME MEASURE Prevalence of miscarriage before 16 weeks' gestation. RESULTS 121 of 1214 women (10.0%, 95% confidence interval 8.3% to 11.7%) miscarried before 16 weeks. 174 of 1201 women (14.5%, 12.5% to 16.5%) had bacterial vaginosis. Compared with women who were negative for bacterial vaginosis those who were positive had a relative risk of miscarriage before 16 weeks' gestation of 1.2 (0.7 to 1.9). Bacterial vaginosis was, however, associated with miscarriage in the second trimester at 13-15 weeks (3.5, 1.2 to 10.3). Only 29 women (2.4%, 1.5% to 3.3%) had chlamydial infection, of whom one miscarried (0.32, 0.04 to 2.30). CONCLUSION Bacterial vaginosis is not strongly predictive of early miscarriage but may be a predictor after 13 weeks' gestation. The prevalence of Chlamydia was too low to assess the risk, but it is unlikely to be a major risk factor in pregnant women.