Bacterial vaginosis is caused by the overgrowth of bacteria that normally live in the vagina. Often, women with bacterial vaginosis have no symptoms, but some women have vaginal discharge, odor, or itching. Studies show that pregnant women with bacterial vaginosis are more likely than women without the condition to have babies that are premature or low birthweight. Doctors can test for the condition by swabbing the cervix during pelvic examination and sending the swabs to the laboratory. To treat bacterial vaginosis, a woman takes an antibiotic either by mouth or by a gel inserted into the vagina. Because poor pregnancy outcomes are associated with bacterial vaginosis and because screening (that is, testing for the condition in people who have no symptoms) and treatment for the condition are easy to perform, some experts favor screening all pregnant women for bacterial vaginosis. However, it is unclear whether screening pregnant women for bacterial vaginosis and treating those with the condition actually improve pregnancy outcomes.