Group B Streptococcus (GBS) is a common bacterium that typically causes no symptoms or harm in adults. However, its presence during pregnancy is important due to the potential for transmission to newborns during childbirth, which can lead to serious health issues for the baby.
Understanding Group B Streptococcus
Group B Streptococcus (Streptococcus agalactiae) is a bacterium often found in the digestive and lower genital tracts of healthy individuals. It is not a sexually transmitted infection, and its presence does not indicate poor hygiene. Many adults carry GBS without experiencing symptoms or illness.
About 1 in 4 pregnant individuals (25-30%) carry the bacteria in their vagina and rectum. This colonization can be temporary, meaning the bacteria may come and go.
Assessing GBS Risk in Pregnancy
The term “GBS score” refers to the clinical assessment of risk for GBS transmission to a newborn, rather than a specific numerical score. A primary method for this assessment involves routine screening through a vaginal and rectal swab culture. This test is usually conducted late in pregnancy, between 36 and 37 weeks of gestation, to determine if the bacteria is present.
A “positive” result from this culture indicates the presence of GBS, while a “negative” result suggests it is not detected at the time of the test. Other clinical factors also play a role in assessing risk and may prompt intervention. These include preterm labor (before 37 weeks), rupture of membranes for 18 hours or more, fever during labor (38°C or higher), or a history of a previous baby with GBS disease.
Protecting the Newborn
When GBS risk is identified, the main strategy to protect the newborn is intrapartum antibiotic prophylaxis (IAP), which involves administering intravenous (IV) antibiotics during labor. This approach aims to reduce the chance of GBS transmission from the birthing parent to the baby. The antibiotics work by reducing the amount of GBS bacteria in the vaginal area during labor, lowering the baby’s exposure as they pass through the birth canal.
Antibiotics are typically given every four hours until delivery, to achieve sufficient levels in the birthing parent’s system before birth. Penicillin G is the preferred antibiotic, with ampicillin as an acceptable alternative. For individuals with a penicillin allergy, other antibiotics like cefazolin, clindamycin, or vancomycin may be used, depending on the severity of the allergy and susceptibility testing.
Potential Impact on Newborns
If GBS is transmitted to a newborn and causes an infection, it can lead to serious complications. These infections are categorized into two main types: early-onset GBS disease and late-onset GBS disease. Early-onset disease occurs within the first week of life, often appearing within hours of birth.
Late-onset GBS disease develops after the first week of life, typically up to three months of age. Both types can lead to severe conditions, including sepsis (a bloodstream infection), pneumonia (a lung infection), and meningitis (an infection of the fluid and lining around the brain and spinal cord). While rare, these complications can be life-threatening or result in long-term health issues such as hearing problems, learning difficulties, or cerebral palsy.