Bacterial vaginosis (BV) is a bacterial infection in the vagina. A healthy vagina contains a balance of both "good" (healthy) and "harmful" (unhealthy) bacteria. Normally, the good bacteria keep the harmful type under control.

A BV infection happens when the normal balance is upset and more harmful bacteria grow than good bacteria. A BV test checks a sample of vaginal discharge (fluid that comes out of the vagina) to look for harmful bacteria.

Any woman can get BV, even women who have never had sex. But it's most common in women who are sexually active. Sometimes a BV infection doesn't cause symptoms, and it can go away on its own. But serious health problems are linked to untreated BV. If you have symptoms, testing and treatment can help avoid the increased risk of these problems:

• Getting a sexually transmitted disease (STD). BV makes your vagina more acidic than normal, which increases your chance of getting STDs, such as chlamydia, genital herpes, gonorrhea, or HIV. And if you have HIV and BV, you're more likely to pass HIV to your sex partner.
• Preterm birth. If you have a BV infection during pregnancy, it can increase the chance that your baby will be born too early (premature baby) or have a low birth weight (less than 5 and a half pounds). Low birth weight can cause serious health problems for your baby, including difficulty breathing, gaining weight, and fighting infections.

There are different ways to check a sample of vaginal discharge for signs of BV:

• Using a microscope. This is called a "vaginal smear" or a "wet mount." The sample is prepared on a glass slide and checked under a microscope for bacteria, white blood cells, and other cells that are signs of infection.
• Checking for odor. This is called a "whiff test." The sample is mixed with a chemical to see if it makes a strong, fishy odor, which is a sign of BV.
• Testing vaginal pH. This test checks the acidity of the sample. High acidity is a sign of BV. But a pH test alone can't diagnose BV, so it's used with other tests.
• PCR test. This test checks your sample for genetic material from harmful bacteria. It's not used as much as the other three tests, because it's more expensive.

Other names: vaginal pH test, KOH test, wet mount test

A BV test is used to find out if a BV infection is the cause of symptoms that appear to be from a vaginal infection.

You may need testing if you have symptoms of BV. These include:

• An unusual vaginal discharge that can be gray or white. It may also be foamy or watery.
• A strong, fish-like odor, especially after sex
• Pain and/or itching in the vagina
• Itching around the outside of the vagina
• Burning feeling when urinating (peeing)

You may also need a test if you have a female sex partner who has BV or symptoms that could be BV.

A BV test is done much like a pelvic exam:

• You'll take off your clothes below your waist and wear gown or use a sheet as a cover.
• You'll lie on an exam table with your feet in stirrups.
• Your health care provider will use a plastic or metal instrument called a speculum to gently widen your vagina so the cervix can be seen.
• Your provider will use a cotton swab or wooden stick to collect a sample of your vaginal discharge.
• Your provider may examine the sample or send it to a lab for testing.

At-home test kits are available to test for the bacteria that cause BV. The kits include everything you need to collect a sample of vaginal fluid and send it a lab for testing. To get proper care, share your results with your provider.

There are also at-home vaginal pH test kits. These kits use a swab or paper strip that changes color after you moisten it with vaginal fluid. A chart shows you what the color means. A high pH (high acidity) is a sign that you may have BV, but it doesn't mean you have BV for sure. And a normal pH doesn't mean you don't have BV. So, discuss your results with your provider.

Follow the instructions your provider gives you to prepare for this test. For 24 hours before your test, you'll usually need to avoid:

• Using tampons
• Douching (rinsing the vagina with water or other fluid)
• Using creams or medicines in the vagina
• Having vaginal sex

With a BV test from your provider, you may feel some mild discomfort when the speculum is put in your vagina.

Abnormal results from a vaginal smear or a whiff test mean that you have a bacterial infection.

The results of a vaginal pH test will be a number that shows how acidic your vagina is. A pH over 4.5 is high, which means you're more likely to have BV. But a pH test can't diagnose BV.

If your results show you have a BV infection, your provider will probably prescribe antibiotic pills and/or antibiotic creams or gels that you put in your vagina. Medicines that treat BV are safe to use during pregnancy.

Sometimes a BV infection will come back after successful treatment. If this happens, your provider may prescribe different medicine or a different dose of the medicine you took before.

There are no over-the-counter treatments for BV. Treatments for vaginal yeast infections will not help BV and could make your symptoms worse. So, don't try to treat an infection yourself.

If your results show you don't have BV, your provider may do more tests to find the cause of your symptoms.

If you have questions about your results, talk with your health care provider.

BV is not spread through sex between female and male partners. So, if you're diagnosed with BV and have a male sex partner, he will not need to be tested. But the infection can be spread between female sex partners. If you have an infection and your partner is female, she should get a BV test.

Researchers aren't sure how BV spreads, but there are steps you can take that may lower your risk of infection:

• Limit your number of sex partners or don't have sex
• Don't use douches
• Use condoms every time you have sex