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Infections Routine

Bacterial Vaginosis in Pregnancy

Also known as BV, Vaginal dysbiosis. Any point in pregnancy; usually diagnosed when symptoms occur.

Bacterial vaginosis (BV) is the most common vaginal condition in people of reproductive age, and it happens when the normal balance of vaginal bacteria is disrupted. It is not a sexually transmitted infection, though it is linked to sexual activity, and it is not caused by poor hygiene. In pregnancy it usually causes only mild symptoms, a thin discharge and a fishy odor, or none at all, but it is treated when symptoms appear, because it has been linked to some pregnancy complications. It is easily diagnosed and cleared with antibiotics that are safe in pregnancy.

Know the warning signs When to call a provider
How common
About 6% to 19%
Of pregnant people in the US; the most common vaginal condition overall.
When
Any time
Can be present before or during pregnancy; often found when symptoms prompt testing.
Urgency
Routine
Mild and treatable; symptomatic BV in pregnancy is treated with antibiotics.
Outlook
Good with treatment
Clears with antibiotics, though it commonly recurs.

Understanding it

What is bacterial vaginosis in pregnancy?

Bacterial vaginosis is an imbalance of the bacteria that normally live in the vagina. A healthy vagina is dominated by protective lactobacilli, which keep it slightly acidic and hold other organisms in check. In BV, those lactobacilli decline and others, especially Gardnerella, overgrow, producing the characteristic thin discharge and fishy smell, though a large share of people have no symptoms at all.

Two misunderstandings are worth clearing up. First, BV is not a sexually transmitted infection: sexual activity and a new partner can tip the balance, but it is a disturbance of your own bacteria, not something passed like an STI, so partners are not treated. Second, it is not about being unclean, quite the reverse: douching, often done in the name of cleanliness, is a leading cause, since it washes out the protective bacteria. Often no specific trigger is found.

In pregnancy, BV matters a little more than outside it. Symptomatic BV has been linked to early water breaking, preterm birth, and infection of the womb during or after pregnancy. Because of that link, the guidance is to treat any pregnant person with symptoms. Screening people who feel fine is not recommended, since treating symptom-free BV has not been shown to prevent preterm birth.

Diagnosis is simple, from an exam and a sample of vaginal fluid, and treatment is a course of antibiotics, tablets or a vaginal gel or cream, all safe in pregnancy. The one frustration is that BV commonly returns, sometimes needing another course. With unusual discharge, an odor, or irritation, get checked rather than guess, since BV, yeast, and other causes are treated differently.

Symptoms

What are the symptoms?

Many people with BV have no symptoms. When present, the hallmark is a thin discharge with a fishy odor. BV itself is mild; the concern in pregnancy is its association with complications.

Early signs

  • A thin, grayish-white discharge
  • A fishy vaginal odor, often stronger after sex
  • Sometimes itching, irritation, or burning around the vagina
  • Often no symptoms at all, with up to 84% of people unaware they have it

Emergency signs — call 911

  • Leaking or a gush of fluid from the vagina, which could mean the water has broken
  • Regular contractions or cramping before 37 weeks
  • Vaginal bleeding
  • Fever, or foul-smelling discharge with pelvic or belly pain, which can signal infection of the womb

Why it matters

Risks to you and baby

Preterm birth and early water breaking

Symptomatic BV has been linked to early water breaking and preterm birth. This link is the main reason BV is treated when it causes symptoms.

Infection of the womb

BV is linked to infection of the amniotic fluid during pregnancy and of the womb lining after delivery (endometritis). Treating symptomatic BV lowers this concern.

Higher susceptibility to STIs

Losing the protective bacteria makes it easier to acquire sexually transmitted infections, including HIV, if exposed. One more reason to treat it and to use protection.

Mostly a nuisance otherwise

Beyond these associations, BV itself is mild. The discharge and odor are bothersome but not dangerous, and it does no damage. The attention in pregnancy is about the pregnancy links, not the BV itself.

How it's found

How is it diagnosed?

BV is diagnosed from an exam and a sample of vaginal fluid, using established criteria or a lab score. It is tested when symptoms prompt it, not as routine screening.

Clinical criteria (Amsel)

Your provider looks for a combination of features: a thin discharge, a raised vaginal pH, a fishy odor when a drop of solution is added, and clue cells under the microscope. Three of four confirm BV.

Lab score (Nugent)

A Gram stain of the vaginal fluid is scored in the lab; a high score, 7 to 10, indicates BV. This is the gold-standard lab test.

Vaginal fluid sample

A simple swab provides the sample for these tests and helps distinguish BV from yeast or other causes of discharge, which are treated differently.

When you have symptoms such as unusual discharge or odor. Routine screening of pregnant people without symptoms is not recommended.

Treatment

How is it managed?

BV is treated with antibiotics that are safe in pregnancy, given to any pregnant person with symptoms. Recurrence is common and may need repeat treatment.

Treatment paths

Treatment is a course of antibiotics: metronidazole by mouth or as a vaginal gel, or clindamycin as a vaginal cream. The same regimens used outside pregnancy are used in it and are considered safe. All symptomatic pregnant people are treated, because of the link between symptomatic BV and pregnancy complications.

Medication

Metronidazole, oral or vaginal, and clindamycin cream are the standard options. Your provider will choose based on your situation. Finishing the full course is important even if symptoms ease quickly.

Monitoring

Symptoms usually resolve within days of starting treatment. Because BV commonly recurs, let your provider know if it comes back, as another course or a longer regimen may be used.

Can it recur?

Yes, frequently, up to 80% within several months in the general population, and it recurs in pregnancy too. It is treated again the same way, and avoiding douching and using condoms can help. Treatment does not change your delivery timing.

What you can do

Can it be prevented?

  • Do not douche

    Douching washes out the protective bacteria that keep the vagina in balance, making it a leading cause of BV. The vagina cleans itself; not douching is one of the most effective steps.

  • Use condoms

    Consistent condom use is linked to lower BV and less recurrence, and it also protects against the STIs that BV makes you more susceptible to.

  • Get checked for symptoms

    With unusual discharge, an odor, or irritation, get evaluated rather than self-treating. BV, yeast, and other causes look similar but are treated differently, and in pregnancy it helps to be sure.

  • Finish your treatment

    Complete the full antibiotic course even if you feel better quickly, which gives the best chance of clearing it and reduces an early recurrence.

Who is more at risk

Risk factors

Douching
Rinsing out the vagina disrupts the protective bacteria and is a leading, preventable risk factor for BV.
A new or multiple partners
A new sexual partner, or multiple partners, can upset the vaginal bacterial balance, though BV is not itself sexually transmitted.
Not using condoms
Condomless sex is linked to higher BV risk; condoms to lower.
A natural lack of lactobacilli
Some people naturally have fewer of the protective lactobacilli, which makes BV more likely. Recent antibiotic use and smoking also raise the risk.

Do not wait

When to call your provider or 911

  • Call your provider if you have unusual vaginal discharge, a fishy odor, or vaginal irritation, so it can be tested and treated.
  • Seek urgent care for leaking or a gush of fluid, which could mean your water has broken.
  • Go in for regular contractions or cramping before 37 weeks.
  • Seek care for a fever, or foul-smelling discharge with pelvic or belly pain, which can signal infection.
  • Let your provider know if BV comes back after treatment, as a repeat or longer course may be needed.

Talking to your team

Questions to ask your provider

  • Is my discharge from BV, a yeast infection, or something else?
  • Which antibiotic is best for me during pregnancy?
  • Does having BV raise my risk of preterm birth?
  • What can I do to keep it from coming back?
  • Should my partner be treated? (Usually no, but ask to be sure.)
  • If it recurs, what is the plan?

Keep reading

More on bacterial vaginosis in pregnancy

All pregnancy guides articles

Good to Know

Bacterial Vaginosis in Pregnancy FAQs

Common questions about bacterial vaginosis in pregnancy, answered.

Is bacterial vaginosis a sexually transmitted infection?

No. BV is an imbalance of your own vaginal bacteria, not something passed between people. Sexual activity and a new partner can tip the balance, but it is not an STI, partners are not treated, and it is no sign of poor hygiene or infidelity.

Did I cause it by not being clean enough?

No, the opposite in one respect: douching, often done to feel cleaner, is a leading cause because it strips out the protective bacteria. Often no specific cause is found, and it is nothing to feel ashamed of.

Will BV hurt my baby?

BV itself is mild, but symptomatic BV has been linked to early water breaking, preterm birth, and infection of the womb, which is why it is treated when it causes symptoms. Most people with BV still go on to healthy pregnancies.

Is the treatment safe in pregnancy?

Yes. The standard treatments, metronidazole by mouth or as a vaginal gel and clindamycin cream, are considered safe, the same regimens used outside pregnancy. Finishing the full course gives the best chance of clearing it.

Why wasn't I screened for it earlier?

Because routine screening of people without symptoms is not recommended: studies have not shown that treating symptom-free BV prevents preterm birth. Testing is done when symptoms appear, which is the time to be tested and treated.

It keeps coming back. Why?

Recurrence is the most frustrating thing about BV: it returns in a large share of people, up to 80% within several months, because the bacterial balance is easily disrupted again. It is treated the same way; avoiding douching and using condoms can reduce how often it recurs, and your provider may use a longer course for frequent recurrences.

How is it different from a yeast infection?

They are different problems with different treatments. BV typically causes a thin, grayish discharge with a fishy odor; a yeast infection, a thick, white, cottage-cheese-like discharge with itching and no strong odor. Because they can look alike, a quick test tells you which it is, especially in pregnancy.

Should my partner be treated too?

Usually not. Because BV is a disturbance of your own bacteria rather than an STI, treating a male partner has not been shown to help and is not routinely done. With a female partner, discuss it with your provider, as the guidance there is evolving. Condoms can help prevent recurrence.

Medically Reviewed · Updated

Reviewed by Dr. Grace Lin, MD, FACOG · OB-GYN

Obstetrician-gynecologist focused on reproductive and sexual health for women: pregnancy, BV, yeast, trichomoniasis and HPV/cervical screening. Our editorial guidelines →

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