Women, men and children of all ages can be colonized with Group B streptococcus (GBS) bacteria without having any symptoms. Group B streptococcus are particularly found in the gastrointestinal tract, vagina and urethra. This is the situation in both developed and developing countries. About one in 2000 newborn babies have GBS bacterial infections, usually evident as respiratory disease, general sepsis, or meningitis within the first week. The baby contracts the infection from the mother during labor. Giving the mother an antibiotic directly into a vein during labor causes bacterial counts to fall rapidly, which suggests possible benefits but pregnant women need to be screened. Many countries have guidelines on screening for GBS in pregnancy and treatment with antibiotics. Some risk factors for an affected baby are preterm and low birthweight; prolonged labor; prolonged rupture of the membranes (more than 12 hours); severe changes in fetal heart rate during the first stage of labor; and gestational diabetes. Very few of the women in labor who are GBS positive give birth to babies who are infected with GBS and antibiotics can have harmful effects such as severe maternal allergic reactions, increase in drug-resistant organisms and exposure of newborn infants to resistant bacteria, and postnatal maternal and neonatal yeast infections.

This review finds that giving antibiotics is not supported by conclusive evidence. The review identified four trials involving 852 GBS positive women. Three trials, which were more than 20 years old, compared ampicillin or penicillin to no treatment and found no clear differences in newborn deaths although the occurrence of early GBS infection in the newborn was reduced with antibiotics. The antibiotics ampicillin and penicillin were no different from each other in one trial with 352 GBS positive women. All cases of perinatal GBS infections are unlikely to be prevented even if an effective vaccine is developed.