OBJECTIVE: To estimate whether bacterial vaginosis, as defined by either Nugent score or vaginal pH, predicts gestational age at delivery in women at risk for recurrent preterm birth. STUDY DESIGN: Planned secondary analysis of a randomized cerclage trial in women with prior spontaneous preterm birth 17 0/7-336/7 weeks. Vaginal Gram stain and pH were collected at the initial study visit. Women not assigned to cerclage, either because they did not experience cervical shortening <25 mm or because they were randomly assigned to no cerclage, were studied. RESULTS: Seven hundred eighty-six women had complete delivery gestational age, Gram stain, and pH results. The diagnosis of bacterial vaginosis by either Nugent score ≥ 7 or by pH ≥ 5 was not associated with earlier birth. CONCLUSION: The presence of bacterial vaginosis at 16-216/7 weeks does not predict gestational age at birth in women at risk for recurrent preterm birth. © 2011 Mosby, Inc.