Group B Streptococcus (GBS) prophylaxis in pregnant women involves preventive measures taken during pregnancy or labor to protect newborns from GBS infection. This intervention is a standard part of prenatal care, aiming to reduce the risk of serious health issues in infants that can arise from exposure to this common bacterium during birth.
Understanding Group B Streptococcus
Group B Streptococcus, or GBS, is a type of bacteria commonly found in the gastrointestinal and genitourinary tracts of humans. It is estimated that between 11% and 35% of pregnant women carry GBS without symptoms. GBS is considered a transient bacterium, meaning its presence can fluctuate over time.
GBS is not a sexually transmitted infection and does not spread through food or water. While generally harmless to adults, GBS poses a risk to newborns. The bacteria can pass from a pregnant person to their baby during vaginal delivery or if the bacteria travel upwards into the uterus after the membranes rupture.
For newborns, GBS infection can lead to severe conditions, collectively known as Group B Strep disease. These include sepsis (a bloodstream infection), pneumonia (a lung infection), or meningitis (an infection of the fluid and lining surrounding the brain). Early-onset GBS disease typically manifests within the first week of life, often within 24 hours of birth. Late-onset GBS disease, though less common, can develop between seven days and three months after birth, with meningitis being a more frequent outcome in these cases.
Screening for GBS
Screening for GBS is a routine part of prenatal care for pregnant women. This test is typically performed late in pregnancy, usually between 36 and 37 weeks of gestation. The timing is important because GBS colonization can fluctuate, so testing closer to delivery provides the most accurate picture of the mother’s status at birth.
The screening involves collecting samples using a sterile cotton swab from both the lower vagina and the rectum. This can be done by a healthcare provider or the pregnant individual. The collected samples are then sent to a laboratory for culture to determine if GBS bacteria are present.
A positive GBS test result indicates the bacteria are present in the vagina or rectum at the time of the test. This means the pregnant person is a carrier and has an increased risk of transmitting the bacteria to their baby during birth. A positive test does not mean the mother is sick or has an infection, only that the bacteria are present. If a pregnant person tests negative, GBS is not detected in the tested areas, significantly reducing the likelihood of transmission at birth. However, due to the transient nature of GBS, a small percentage of women who test negative may become positive by the time of labor.
Prophylaxis During Labor
GBS prophylaxis primarily involves intravenous (IV) antibiotics during labor. This intervention aims to reduce the risk of GBS transmission from the pregnant parent to the newborn. Penicillin or ampicillin are the most commonly used antibiotics, both of which are beta-lactam antibiotics. Alternative antibiotics, such as cefazolin or vancomycin, are available for individuals with penicillin allergies.
The goal of this treatment is to achieve sufficient antibiotic levels in the mother’s system to effectively reduce the bacterial load during birth. Antibiotics are started as soon as labor begins or when the amniotic sac ruptures. For optimal effectiveness, it is recommended that antibiotics be administered for at least four hours before delivery. This timing helps ensure adequate antibiotic concentration to protect the baby as they pass through the birth canal.
Antibiotics are given intravenously because oral antibiotics taken before labor are not effective in preventing GBS transmission, as the bacteria can quickly recolonize. Prophylaxis is not needed for a planned Cesarean section if labor has not started and the membranes are intact, as the risk of transmission is very low.
Impact and Important Considerations
GBS prophylaxis has had a significant impact on newborn health, greatly reducing the incidence of early-onset GBS disease. Before widespread screening and prophylaxis guidelines were implemented, early-onset GBS disease occurred in about 1.5 to 1.8 cases per 1,000 live births. With current preventive strategies, this rate has decreased to approximately 0.2 to 0.23 cases per 1,000 live births. This intervention can reduce a baby’s chance of developing GBS disease from about 1 in 200 to 1 in 4,000 if the mother receives appropriate antibiotics during labor.
Despite its effectiveness, there are considerations regarding GBS prophylaxis. While generally safe, some women may experience mild side effects from antibiotics, such as nausea, vomiting, or diarrhea. Severe allergic reactions, including anaphylaxis, are rare but can occur, highlighting the importance of informing healthcare providers about any known allergies. Ongoing discussions and research regarding the potential impact of intrapartum antibiotics on the newborn’s developing gut microbiome, though the long-term clinical significance is still being studied.
Prophylaxis primarily targets early-onset GBS disease, and it does not prevent late-onset GBS infections, the cause of which is not fully understood. In scenarios where prophylaxis is missed or less effective, such as rapid labor where antibiotics cannot be administered for the recommended four hours, or if a mother goes into labor before GBS status is known, newborns are closely monitored for any signs of infection. Despite these considerations, the widespread adoption of GBS screening and intrapartum antibiotic prophylaxis has led to a significant reduction in severe GBS infections and associated morbidity and mortality in infants.