BV in pregnancy is a common bacterial imbalance that's linked to preterm delivery and low birth weight. It's safely treated with oral metronidazole or vaginal metronidazole gel or clindamycin cream. Tell your prenatal provider about any unusual discharge or fish-like odor, and finish the full antibiotic course. If you've had a preterm birth before, ask about screening.
most common cause of discharge, ages 15–44
but linked to sex
or clindamycin
| Item | Value |
|---|---|
| US women affected | ~29% — most common cause of discharge, ages 15–44 |
| Recurs within 12 mo | >50% |
| An STI? | no — but linked to sex |
| Cure | metronidazole — or clindamycin |
What BV is and why pregnancy changes the stakes
Bacterial vaginosis happens when the normal, acid-producing Lactobacillus bacteria that keep the vagina healthy get crowded out by a mix of anaerobic bacteria. That shift drops the vagina's protective acidity and lets the overgrowth take hold. It's the most common vaginal condition in women ages 15 to 44 CDC, and it shows up whether or not you're pregnant. During pregnancy the same imbalance carries higher stakes for the baby, so providers pay closer attention to it.
BV isn't classified as a traditional sexually transmitted infection, though it's strongly tied to sexual activity. Women who've never been sexually active rarely get it. Risk rises with douching, not using condoms, and new or multiple partners, including female partners. You can't catch it from toilet seats, bedding, or swimming pools. If you're unsure whether your symptoms point to BV or thrush, the discharge and odor differ in telling ways, which we break down in yeast infection vs bv.
Why BV matters in pregnancy
The same loss of protective lactobacilli that defines BV changes the entire vaginal environment, and that environment isn't sealed off from the pregnancy. The anaerobic overgrowth can trigger low-grade inflammation and produce enzymes that may weaken the membranes and the cervix. That's how an apparently minor discharge problem connects to outcomes that matter. The bacteria and the inflammatory response they provoke don't stay contained to a vaginal nuisance.
Many people with BV have no symptoms at all. In pregnancy you can carry the imbalance without the classic thin gray discharge or the fish-like odor that's strongest after sex. When symptoms do appear, they can include itching, burning, or burning when you urinate. Because the quiet cases are common, what you feel isn't a reliable gauge of whether BV is present.
Risks to the baby
In pregnancy, BV is associated with a higher risk of preterm delivery (birth before the pregnancy reaches full term) and low birth weight (a baby born smaller than expected) CDC STI Tx Guidelines, 2021. These are associations, not guarantees, and most people with BV go on to deliver healthy, full-term babies. The link is consistent enough that it shapes how clinicians screen and treat during pregnancy.
BV also raises the risk of acquiring or transmitting HIV and other STIs. A meta-analysis of more than 30,000 women found that BV increased the risk of acquiring HIV by about 60 percent (RR 1.61), driven by that same loss of protective lactobacilli Atashili et al.. In pregnancy, where any new infection has downstream consequences, that vulnerability is one more reason not to leave BV unaddressed.
Screening for BV in pregnancy — and when
Diagnosis is straightforward: a clinician examines the discharge and runs simple in-office tests on a vaginal sample, sometimes confirmed by a lab. The full process, including what the swab feels like, what the results mean, and how BV is told apart from yeast and trichomoniasis, is covered in bv testing. If you have symptoms during pregnancy, get evaluated rather than self-treating, since the look-alikes are treated differently.
Routine BV screening of all pregnant people without symptoms isn't recommended, because treating symptom-free BV hasn't reliably reduced preterm birth across studies. The picture differs if you have symptoms, or in some cases if you've had a previous preterm delivery, when your provider may test and treat. Bring it up at a prenatal visit; this is a judgment call best made with your obstetric clinician, not from a search result. If your concern is about a recent exposure to another infection rather than BV itself, see when to test after exposure for timing.
Safe treatment of BV in pregnancy
The options in pregnancy are the same first-line antibiotics used outside of it, with a long track record. Oral and vaginal regimens are both used; your provider will pick based on your symptoms, preferences, and history. The standard choices are below.
| Regimen | How it's taken | Notes for pregnancy |
|---|---|---|
| Metronidazole 500 mg oral | Twice daily for 7 days | Treats the whole body; well-studied in pregnancy |
| Metronidazole 0.75% gel | One 5 g applicator intravaginally daily for 5 days | Localized; lower systemic exposure |
| Clindamycin 2% cream | Intravaginally at bedtime for 7 days | Oil-based — can weaken latex condoms |
A few practical points matter as much as the prescription itself. Finish the entire course even after symptoms ease, since stopping early is one of the most common reasons BV bounces back. Per the 2021 guidelines, avoiding alcohol while on metronidazole isn't necessary, since there's no convincing evidence of a reaction. Clindamycin cream and ovules are oil-based and can weaken latex condoms, so don't rely on latex for protection while using them. For the full breakdown of regimens, recurrence strategies, and what to do if it keeps returning, see bv treatment.
Recurrence is common. Standard antibiotics cure 80 to 90 percent of acute episodes, but it returns in up to 60 percent of women within 12 months SASGOG. When it happens three or more times in a year, that's recurrent BV, and it usually calls for a months-long maintenance plan rather than another single course. In pregnancy especially, tell your provider if symptoms come back so the approach can be adjusted.
Reducing transmission and risk around delivery
Routine treatment of male partners isn't recommended and doesn't prevent recurrence, so a male partner generally doesn't need a prescription. With a female partner it's worth raising, since shared imbalance can play a role; ask whether partner treatment makes sense in your situation so you're not passing it back and forth. The aim is to clear the imbalance before delivery and keep it cleared, which means completing treatment and following up.
For prevention going forward, the levers are simple: skip douching, which disrupts the protective bacteria, and use condoms every time, since they lower risk for the sexually transmitted infections that often travel alongside BV. Because so many cases are silent, routine testing catches what symptoms miss. If you're due for a broader check, you can get tested.
When to see a clinician
Contact your prenatal provider if you notice a new thin gray or white discharge, a strong fish-like odor, itching, burning, or burning when you urinate. Reach out promptly if you've had a previous preterm birth and develop symptoms, if symptoms return after treatment, or if you're unsure whether what you have is BV, a yeast infection, or something else. During pregnancy there's no downside to asking, and a quick evaluation settles it.