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Prenatal Group B Strep (GBS) Screening

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Also known as: Group B Beta-hemolytic Streptococcus; Group B Streptococcus; Group B Strep; GBS; Strep Group B; Streptococcus agalactiae; Beta-hemolytic Strep Culture
Formal name: Prenatal Group B Streptococcus Screening

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The Test Sample

What is being tested?

Group B strep (GBS) is the common name for the bacterium Streptococcus agalactiae that can be present (colonizing) in the digestive tract and genital tract. It rarely causes symptoms or problems in healthy adults but can cause infections and serious illness in newborns who become infected before or during labor and delivery. GBS screening identifies the presence of the bacteria in the vaginal/rectal area of a pregnant woman.

GBS can cause early-onset GBS disease that occurs within the first week after birth. Signs and symptoms in newborns include fever, difficulty with feeding and breathing, irritability or lethargy, and a blue tint to the skin. GBS can cause serious infections such as pneumonia, sepsis, and meningitis. According to the Centers for Disease Control and Prevention, it is the most common cause of life-threatening infections in newborns.

Approximately 25% of pregnant women carry group B strep in their rectum or vagina. However, the number of infants with GBS disease has decreased significantly in recent years because of a concerted effort by healthcare practitioners to screen pregnant women for GBS late in their pregnancy and, when they are positive for GBS, to treat them with intravenous antibiotics (usually penicillin or ampicillin) during labor. This prevents or greatly decreases the risk of passing the bacteria to the newborn. Nevertheless, GBS disease remains the primary cause of early-onset sepsis, a serious and life-threatening infection in newborns.

Currently there is no vaccine available to prevent GBS, and treating all pregnant women with antibiotics is not practical. Screening for GBS and appropriate treatment continues to be the best means for preventing GBS disease in newborns.

How is the sample collected for testing?

For screening pregnant women, a swab is typically obtained from the vagina and rectum. Urine collected during pregnancy may be cultured for significant numbers of GBS.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.