Group B Streptococcus (GBS) is a type of bacteria found in the lower genital tract of about 25 percent of all women. GBS infection usually causes no problems in women before pregnancy, but it can cause serious illness in the mother during pregnancy. GBS may cause chorioamnionitis (a severe infection of the placental tissues) and postpartum infection. Urinary tract infections caused by GBS can lead to preterm labor and birth or kidney infection and sepsis.
GBS is the most common cause of life-threatening infections in newborns, including pneumonia and meningitis. Newborn babies can contract the infection during pregnancy or from the mother's genital tract during labor and delivery.
The Centers for Disease Control and Prevention recommends screening of all pregnant women for vaginal and rectal GBS colonization between 35 to 37 weeks' gestation. This screening is called a GBS culture.
The screening test is important because it helps identify women who should be treated for GBS. Mothers should be treated if they have certain risk factors, such as having a medical condition that impairs the immune system, like diabetes, HIV infection, cancer or liver disease, or having had positive results from the GBS culture. Treating pregnant women for GBS helps reduce their risk of transmitting GBS to their babies. Babies whose mothers receive antibiotic treatment for a positive GBS test are 20 times less likely to develop the disease than those without treatment.