Rationale for screening and treating asymptomatic women The rationale for treating asymptomatic bacterial vaginosis (Nugent score 7-10) and asymptomatic intermediate flora (Nugent score 4-6) is based on data: 1) showing their association with adverse pregnancy outcomes[38], and 2) several promising trials showing that treatment may reduce preterm birth[39, 40]. Up to 84% of bacterial vaginosis cases are asymptomatic [23]. In a meta-analysis of 32 studies in developed and developing countries by Leitich et al, asymptomatic BV (Nugent score 7-10) was associated with a 6.32 times elevated risk of late miscarriage (95% CI 3.65-10.94) and 2.16 times (95% CI 1.56-3.00) increased risk of preterm birth. The association with preterm birth was higher when BV was detected in early pregnancy (<16 weeks, OR 2.97, 95% CI 1.48-5.98)[38]. Among women with a prior history of preterm birth, Hauth and colleagues found that screening and treatment of asymptomatic BV (Nugent score 7-10) with metronidazole and erythromycin at 22 weeks gestation significantly reduced the incidence of preterm birth from 46% in the placebo group to 31% in the treatment group [41]. In the multi-center NICHD BV trial, 1953 women with asymptomatic BV between 16-24 weeks of gestation were randomized to receive two doses of metronidazole (2g) or placebo; however, treatment did not significantly affect preterm delivery or other adverse perinatal outcomes [42].