What Is a Strep B Test?

During pregnancy, a woman who undergoes standard clinic and medical care usually has multiple tests done to ensure her health and the health of her baby. These tests can include genetic screening through blood tests or amniocentesis, glucose and protein monitoring through urine samples, and the reading of blood pressure. However, another test that is done for pregnant women is the group B strep test. The sections below explain what the test is, why it's recommended and more.

The Test Defined

• The group B strep test refers to the testing of an individual for the streptococcus bacteria. The test tests for only the "B" classification of streptococcus, and does not indicate whether type "A" streptococcus is present. The test is administered most commonly to pregnant women as part of their prenatal care.

What is Group B Strep?

• Group B strep, the bacteria detected by the group B test, is a bacteria that is found in the reproductive and digestive tracts of up to 30 percent of women. Most of the time, the women who have the bacteria don't even know it because they have no symptoms, and no treatment is necessary because the woman is simply a carrier for the bacteria and does not become ill. The bacteria, however, can lead to blood, urinary tract and skin infections that can be serious if left untreated.

When Is It Done?

• The test for group B strep is usually given to pregnant women in their third trimester, typically at 35 to 37 weeks. This is done because it is possible to pass the bacteria to the baby during labor, so physicians want to know whether to take precautions against this possibility. Despite the fact that a woman can test positive for the bacteria at some times and not at others, most doctors automatically assume that the presence of the bacteria will be repeated in women who previously have tested positive. The test thus isn't administered more than once if a woman receives a positive test result.

Why Is It Done?

• The group B test is done because of the risks for infection, not only to the pregnant woman, but especially to the baby. Group B can cause serious conditions in newborns, such as meningitis and sepsis, which can lead to other problems such as blindness or, in rare cases, even death. However, these problems occur in a small number of cases--only 0.5 to 1 percent of infants born to mothers with group B strep (GBS) develop such symptoms of early-onset GBS disease.

What If The Test Is Positive?

• If your test for GBS is positive, then your doctor will probably prescribe an oral antibiotic. During labor, you will be placed on an intravenous antibiotic that will take care of any bacteria in the genital tract not killed by the oral antibiotic.

What Is the Test Like?

• The test for group B strep is a simple vaginal culture that is taken with a swab during a vaginal exam. You will be asked to undress, put on a gown and lie on the exam table. The doctor will wipe the inside of your vagina with the swab, which later will be sent to a lab for analysis. The test does not hurt and takes only a few seconds. Since most pregnant women have a pelvic exam during late pregnancy to assess the cervix anyway, most doctors simply do the test during that exam with your consent.