Frequently confused with Group A streptococcus, which causes strep throat, Group B strep is a bacterium that is present in the vagina and gastrointestinal areas of 10% to 30% of pregnant women, though it rarely causes an infection. It is usually not a problem, except when it is present in the vagina during delivery. In this case, it can spread to infect the uterus, amniotic fluid, urinary tract, and any incision made during a cesarean section. At delivery, when the baby passes through the birth canal, the bacteria can be inhaled or ingested.

Infected infants may display symptoms within six hours of birth or as late as two months of age. If untreated, the baby may become septic (infection in blood), develop pneumonia, suffer hearing or vision loss, or develop varying degrees of physical and learning disabilities.

To best assess the risk of infecting the baby at delivery, the mother is screened for Group B strep between 35 and 37 weeks gestation. Specimens from the mother’s vaginal and rectal areas are collected and within 24 to 48 hours the laboratory can determine if Group B strep bacteria are present. If the bacteria are present, or if the woman goes into labor before testing can be completed, it is recommended that the woman receive antibiotics intravenously during labor. Treatment with oral antibiotics taken prior to labor has not proven to be effective in preventing Group B strep infections in the newborn.

Limitations of Group B strep screening:
The screen may not detect a small percentage of women with Group B strep.

Labor may begin before the test results are available.