Natural history of group B streptococcus colonization and its therapy during pregnancy.

Seven hundred twenty-two pregnancies were studied in a private-practice setting to determine the natural history of colonization by group B streptococcus (GBS) over time. The colonization rate remained constant at 7% to 8% in each trimester, with 19% of the women colonized at some time during pregnancy. The organism was lost spontaneously at some time during pregnancy in 51%. Treatment of third-trimester pregnant women and their husbands with penicillin G resulted in a significant reduction in GBS colonization at delivery as compared to an untreated control group. If other factors are considered, however, routine culturing for GBS in pregnant women and treatment of those harboring the organism with penicillin G are not recommended.