Bacterial vaginosis (BV) is an infection caused by an imbalance of bacteria in the vagina; it's most common among women who douche or who have multiple sexual partners. BV is very common -- as many as 16 percent of pregnant women have it -- but it often has no signs. Without proper treatment, having bacterial vaginosis during pregnancy can increase your risk of miscarrying in the second trimester and raise your chances of delivering prematurely. Sometimes, the main signs can mimic those of a yeast infection (like itching, discharge with a strong odor, and a burning feeling when you pee), so it's important to see your doctor if you have any symptoms. Antibiotics can easily clear up BV, so the sooner you're diagnosed the better.
Testing for BV is not a routine part of prenatal care, but doctors sometimes test women who have a high risk of preterm labor (such as those who delivered prematurely in a previous pregnancy) or other health conditions associated with preterm birth, just to be safe.