A Group B Strep (GBS) screening test is conducted late in pregnancy to identify the presence of a common bacterium. This procedure helps healthcare providers determine if preventative action is needed before delivery. The primary goal is to minimize the risk of a severe infection being transmitted to the newborn during birth.
Understanding the Need for Screening
The screening targets Group B Streptococcus, a type of bacteria that frequently lives in the gastrointestinal and genitourinary tracts of healthy adults. Approximately one in four pregnant individuals naturally carry GBS, often without any symptoms or illness themselves. This colonization is usually harmless to the mother, but it poses a potential risk to the baby during a vaginal delivery as the infant passes through the birth canal.
If the baby is exposed to the bacteria and becomes infected, the consequences can be serious. GBS is a leading cause of life-threatening infections in newborns, known as early-onset disease. These rare but severe infections include sepsis (blood infection), pneumonia (lung infection), and meningitis (infection of the fluid and membranes surrounding the brain and spinal cord). Screening allows for timely intervention, which reduces the chance of the infant developing GBS disease.
How the Procedure is Performeda
The GBS screening is typically scheduled late in the third trimester, between the 35th and 37th weeks of pregnancy. This timing is chosen because the presence of the bacteria can be intermittent, and testing close to delivery provides the most accurate reflection of colonization status at birth. The procedure itself is quick, painless, and involves collecting a sample from two specific areas.
A healthcare provider uses a sterile cotton swab to collect secretions from the lower vagina and the rectum. A speculum is not needed for this collection, and some individuals may be given the option to perform the swabbing themselves. Once collected, the swab is sent to a laboratory where the sample is placed in a special culture medium to see if Group B Streptococcus bacteria grow.
Interpreting the Results and Treatment
A “positive” result indicates that GBS bacteria were detected in the swab sample, meaning the individual is colonized at that time. A positive result does not mean the person is sick or has an infection, but that they are a carrier and preventative measures are needed during labor. Conversely, a “negative” result means the bacteria were not detected, and no treatment is necessary.
For a positive screening result, the standard course of action is to administer intravenous (IV) antibiotics during labor to protect the baby. The medication, typically penicillin or a related antibiotic, is given through a vein every four hours until delivery. This ensures a high concentration of the antibiotic is in the mother’s system when the baby is most at risk. This preventative use of antibiotics lowers the risk of the newborn developing early-onset GBS disease. Treatment is also recommended if GBS was found in a urine culture during pregnancy or if a previous baby had GBS disease.