What have we learned about vaginal infections and preterm birth?

Asymptomatic maternal genital tract infection during pregnancy, particularly bacterial vaginosis, has been consistently associated with preterm birth. In response to this evidence, the Maternal-Fetal Medicine Units Network (MFMU) designed and conducted 2 large randomized, placebo-controlled clinical trials of metronidazole treatment of asymptomatic pregnant women with bacterial vaginosis or trichomoniasis in a general obstetrical population. These studies showed that treatment of women with bacterial vaginosis failed to prevent preterm birth, regardless of their history of prior preterm birth. Metronidazole treatment of women with trichomoniasis significantly increased the risk of preterm birth compared to placebo. These results formed the basis of the US Preventive Services Task Force recommendation that screening for bacterial vaginosis not be undertaken in low-risk pregnant women, and show that MFMU network studies can have a direct and immediate impact on obstetrical practice.