There are many different kinds of bacteria growing in your vagina. These bacteria are completely normal and actually protect the vagina. However, bacterial vaginosis (BV) is caused by an imbalance of these different kinds of bacteria. The most common is an overgrowth of gardnerella vaginalis.
BV is the most common vaginal infection in people of childbearing age. BV is also very common among pregnant people. This can be dangerous because BV during pregnancy has been linked to higher rates of miscarriage (particularly in the first trimester). BV is also associated with premature delivery, low birth weight, and pelvic inflammatory disease. For all these reasons, it is important to talk to a health care professional if you think you may have BV. You can get tested for BV at your local Planned Parenthood health center.