While it is clear that intrapartum antibiotics reduce neonatal GBS infection rates, the mechanism by which these drugs prevent neonatal GBS is not well established. One postulated theory is antibiotics work to reduce bacterial load in the birth canal; thus decreasing fetal exposure during labor and delivery. To our knowledge, the relationship between vancomycin and vaginal GBS colony counts has never been studied. In this prospective cohort study, our objective is to determine the relationship between intrapartum IV vancomycin and vaginal GBS colony counts.