Amniorrhexis lowers the incidence of positive cultures for group B streptococci.

Objective: Our purpose was to determine the effect of amniorrhexis on cultures for group B streptococci.

Study Design: Intrapartum vaginal cultures for group B streptococci were obtained before and after rupture of membranes in 166 women; in addition, rectal cultures were obtained from the last 35 patients.

Results: Before rupture of membranes 49 of 166 (30%) of the vaginal cultures were positive for group B streptococci; only 28 of 166 (17%) remained positive after rupture of membranes (p = 0.