Group B Streptococcus (GBS) is a common bacterium found in the gastrointestinal and genitourinary tracts of many healthy adults. While colonization is typically harmless for the person carrying it, it poses a risk to newborns during childbirth. An estimated 10% to 30% of pregnant women carry the bacteria, which can be transmitted to the infant as they pass through the birth canal. This transmission can lead to neonatal GBS disease, a severe infection causing sepsis, pneumonia, or meningitis in the baby’s first week of life. Modern medical strategies focus almost entirely on preventing this transmission through targeted intervention during labor.
The Standard GBS Screening Process
Routine screening late in pregnancy is the primary defense against early-onset neonatal GBS disease. This standardized test is typically performed between 36 weeks and 0 days and 37 weeks and 6 days of gestation. This timing is selected because the results most accurately predict colonization status at the time of delivery.
The screening procedure is simple, quick, and painless, involving the collection of a sample from two specific sites. A sterile swab is used to sample the lower vagina and the rectum. The sample is then sent to a laboratory to be cultured and analyzed for the presence of GBS bacteria.
A positive result means the individual is colonized with GBS but does not mean they are sick or that the baby will definitely be infected. Colonization can be transient, meaning the bacteria may come and go, which is why testing close to the delivery date is necessary. The screening result is the main factor determining the need for preventive antibiotic treatment during labor.
Antibiotic Treatment During Labor
Intrapartum Antibiotic Prophylaxis (IAP) involves administering antibiotics intravenously during the labor process. The goal of IAP is to significantly reduce the bacterial count in the birth canal just before delivery, which is when transmission most often occurs. This prophylaxis is highly effective, reducing the incidence of early-onset GBS disease by up to 82%.
Penicillin G is the medication of choice for IAP, administered in a specific dosing regimen. The standard protocol involves an initial loading dose of 5 million units given intravenously, followed by a maintenance dose of 2.5 to 3.0 million units every four hours until the baby is delivered. This regimen ensures that adequate concentrations of the antibiotic are achieved in the maternal bloodstream, fetal circulation, and amniotic fluid.
Ampicillin is often used as an acceptable alternative to Penicillin G, typically at a loading dose of 2 grams intravenously, followed by 1 gram every four hours until delivery. The timing of administration is crucial; the antibiotics must be given for at least four hours before delivery to be considered fully protective. If the birth occurs in less than four hours, the infant is typically considered at higher risk and requires closer monitoring. For individuals with a severe Penicillin allergy, alternative antibiotics like Clindamycin or Vancomycin may be used, depending on the known susceptibility of the GBS strain.
Prevention Strategies for Specific High-Risk Situations
While the standard protocol relies on a positive GBS screening result, IAP is also recommended in several high-risk scenarios, even if the mother was not screened or tested negative. This approach ensures protection when the likelihood of transmission is elevated.
IAP is warranted if there is a history of a previous infant who developed invasive GBS disease, as the risk of recurrence is high. Another indication is the presence of GBS in the urine (GBS bacteriuria) at any point during the current pregnancy. This indicates a high bacterial load and necessitates IAP regardless of the rectovaginal screening result.
IAP is also recommended if a pregnant person presents in labor before 37 weeks of gestation, or if the membranes have ruptured for 18 hours or more, due to the increased risk of ascending infection. Maternal fever during labor, defined as 100.4°F (38°C) or greater, is a trigger for IAP when the GBS status is unknown. These clinical risk factors bypass the need for a positive screening result.
Addressing Non-Medical Prevention Methods
Many individuals explore non-medical methods to try to eliminate GBS colonization before labor, but these approaches are not supported by current medical guidelines for preventing neonatal disease. Methods like dietary changes, the use of oral probiotics, or topical applications of substances like tea tree oil are often discussed. While some of these alternatives may potentially reduce the level of colonization, GBS can quickly recolonize the area, making any effect short-lived.
Treating colonization with oral antibiotics before labor is also not the standard of care because the bacteria can return rapidly, rendering the early treatment ineffective for preventing transmission at birth. The only proven method to prevent early-onset neonatal GBS disease is the administration of intravenous antibiotics during the delivery process itself. Therefore, while practices like regular hygiene or maintaining a healthy diet support overall wellness, they do not replace the established medical screening and IAP protocols.