If you're pregnant and you're getting a prescription for metronidazole, you already have an increased risk of complication—because you have an infection. Maybe it's something as basic as bacterial vaginosis. If you're not pregnant, BV might be just a passing complication in your life. It's basically just an overgrowth of anaerobic bacteria in and around the vagina, but it's nothing that's not already there. Get it during pregnancy, though, and you could deliver prematurely, which comes with a whole host of other problems like brain bleeds and hearing impairments.