Bacterial vaginosis is a vaginal condition characterized by an abnormal vaginal discharge due to an overgrowth of normal bacteria in the vagina. Women with bacterial vaginosis have less of the normal vaginal bacteria called lactobacilli. Symptoms are the vaginal discharge and sometimes a fishy odor. A sign under the microscope is an unusual vaginal cell called a clue cell. A metanalysis of 18 separate studies involving over 20,000 women demonstrated that bacterial vaginosis predisposes to preterm delivery and the earlier a vaginal infection occurs in pregnancy, the greater is the risk of a preterm delivery. The metanalysis also revealed that bacterial vaginosis increases the risk of a spontaneous abortion nearly 10-fold. Bacterial vaginosis also can lead to infection of the amniotic fluid and of the uterus after delivery. Therefore, screening and treatment for bacterial vaginosis during pregnancy should be routine.