Bacterial vaginosis is caused by a change in the balance of bacteria in the vagina. Normally, there are a lot of "good" bacteria and some "bad" bacteria in the vagina. The good types help control the growth of the bad types. But when you have bacterial vaginosis, there are not enough good bacteria and too many bad bacteria.
Many women with bacterial vaginosis don't have symptoms. The most common symptom is an increase in vaginal discharge. The discharge often has a fishy smell.
Women who have this problem during pregnancy have a higher chance of miscarriage, early delivery, and an infection after delivery. So it's important for pregnant women with symptoms to be tested.
Tests for bacterial vaginosis include:
- Wet mount. A sample of vaginal discharge is checked for bacteria, white blood cells, and unusual cells called clue cells. If clue cells are present, it means you may have bacterial vaginosis.
- Whiff test. A sample of discharge is checked to see if a strong fishy odour is created when a special solution is added. A fishy odour usually means you have bacterial vaginosis.
- Vaginal pH. The pH of a sample of vaginal discharge is measured. Bacterial vaginosis often causes a pH that is higher than normal.
- Oligonucleotide probe. A sample of vaginal discharge is tested for the genetic material, or DNA, of this bacteria. This test is not often used.
Why It Is Done
Tests for bacterial vaginosis are done to help find the cause of symptoms such as abnormal vaginal discharge, irritation, or pain.
How To Prepare
Do not douche, have sex, or use vaginal medicines for 24 hours before this test.
Talk to your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .
How It Is Done
You will take off your clothes below the waist. You'll have a gown to drape around your waist. You will then lie on your back on an examination table. Your feet will be raised and supported by stirrups. This is similar to having a pelvic examination or Pap test.
Your doctor will insert a lubricated tool called a speculum into your vagina. The speculum gently spreads apart the vaginal walls. This allows your doctor to see the inside of the vagina and the cervix.
Samples of fluid inside the vagina are then collected with a swab or wooden stick.
How It Feels
You may feel some discomfort when the speculum is put in, especially if your vagina is irritated and tender.
There is little chance of having a problem from a bacterial vaginosis test.
There is no abnormal discharge in the vagina.
A wet mount does not show clue cells or large numbers of bacteria that cause bacterial vaginosis.
Adding a special solution to a sample of the discharge doesn't cause a fishy odour.
Vaginal pH is in the normal range of 3.8 to 4.5.
There is a thin, greyish white discharge in the vagina.
A wet mount shows clue cells or large numbers of the types of bacteria that cause bacterial vaginosis, or both.
Adding a special solution to a sample of the discharge causes a fishy odour.
Vaginal pH is more than 4.5.
What Affects the Test
You may not be able to have the test, or the test may not be helpful, if:
- You are having your menstrual period.
- You use a vaginal medicine.
- You have sex or you douche in the 24 hours before this test.
What To Think About
- A woman who has bacterial vaginosis during pregnancy has a higher risk of delivering her baby early. So it's important to treat bacterial vaginosis during pregnancy with antibiotics.
- Experts disagree about calling bacterial vaginosis a sexually transmitted infection (STI). But a history of STIs or having multiple sex partners does increase the chance of getting bacterial vaginosis.
- Bacterial vaginosis may be found during a Pap test. But a Pap test is not recommended as a test to find it.
Other Works Consulted
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Current as of: November 8, 2019
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine
Devika Singh MD, MPH - Infectious Disease