group b strep.
Pregnant women today are routinely screened for the presence of Group B Streptococcus (GBS) between 35 and 37 weeks of pregnancy.
If a woman tests positive, the American College of Obstetricians and Gynecologists (ACOG) recommends that antibiotics be administered to the mother during labor. In some cases, babies may also be treated with antibiotics immediately after birth.
Approximately 30 percent of pregnant women carry Group B Streptococcus in their bodies before birth, and between 40 and 75 percent of these mothers may transmit the bacteria to their babies during delivery.¹
However, the actual incidence of Group B Streptococcus disease in newborns is relatively low—estimated to be between 1 and 2 cases per 1,000 live births.² ³
Risk Factors for Transmission
Women are considered at higher risk of transmitting the infection if they develop a fever during labor. However, this measure may not always be reliable.
For example, epidural anesthesia is known to increase maternal temperature, which can lead to a false indication of infection risk.⁴
Premature babies do have a slightly higher risk of developing infection, with an estimated rate of 3.1 cases per 1,000 births.⁵
Routine Use of Antibiotics
Given the relatively low rate of infection, the routine use of antibiotics for mothers and newborns has raised questions among some researchers and clinicians.
Fewer than 2 out of every 1,000 babies develop Group B Streptococcus disease. Yet many healthy babies are exposed to antibiotics shortly after birth as a precaution.
Both mothers and babies may be exposed to risks associated with antibiotic use, including:
Allergic reactions to medications such as penicillin
Disruption of normal bacterial balance
Potential weakening of the immune system
In one reported case, a woman received penicillin during labor because she tested positive for Group B Streptococcus. She experienced a severe allergic reaction that resulted in an emergency cesarean delivery.⁶
As with any medication, the use of drugs during pregnancy and labor carries potential risks.
Effects on Diagnosis
Some research has also suggested that administering antibiotics to mothers during labor may complicate the diagnosis of infection in newborns.
One clinical study found that giving antibiotics during labor did not change the overall course of the disease, nor did it delay the onset of symptoms or treatment in infants who developed infection.⁷
When babies are exposed to antibiotics before birth—through medications given to their mothers—the growth of bacteria in blood cultures taken from the baby after birth may be suppressed.⁸
This can make it more difficult to accurately diagnose infection.
Similarly, administering antibiotics before obtaining blood samples from a newborn may reduce the likelihood of detecting bacteria in infants who are truly ill.⁹ ¹⁰
As a result, babies who are genuinely at risk for complications from early-onset Group B Streptococcus infection may not always be correctly diagnosed.
Observation After Birth
Because of concerns about infection, the American Academy of Pediatrics has recommended that some newborns be observed in the hospital for 48 hours after birth.
However, research suggests that the likelihood of symptoms appearing after the first day of life is extremely low—even when obstetric risk factors are present.
In one study, the rate of infection appearing on the second day of life was only 0.04 percent.¹²
These findings raise questions about whether extended observation in a neonatal nursery is always necessary.
The Role of Breastfeeding and Environment
Another important consideration is whether babies who develop Group B Streptococcus infection are breastfed.
The colostrum that a baby receives in the first hours after birth contains antibodies specifically designed to protect newborns from infection.
Additionally, many of the babies who developed Group B Streptococcus disease in clinical studies were born in hospitals, where exposure to various microbes is more common.
Making Informed Decisions
The issue of Group B Streptococcus screening and treatment continues to generate discussion within the medical community.
While screening and antibiotic treatment are widely recommended as precautionary measures, the relatively low rate of infection and the potential side effects of antibiotic use highlight the importance of careful consideration.
Expectant parents should discuss the risks and benefits of screening and treatment options with their care providers so they can make informed decisions about what approach feels most appropriate for their pregnancy and birth experience.