Prenatal antibiotic treatment does not decrease group B streptococcus colonization at delivery

Objective: To evaluate whether an outpatient antibiotic regimen decreased group B streptococcal (GBS) colonization to preclude the use of intrapartum antibiotics. Methods: A double-blind randomized controlled trial evaluating prenatal oral amoxicillin versus placebo with the primary outcome of GBS colonization at the time of labor. Results: Of those patients receiving both amoxicillin and a repeat culture at the time of labor, 6 of the 14 (43%) tested positive for GBS colonization. Given persistent GBS colonization of 67% (10/15) in the placebo group, treatment with amoxicillin did not significantly impact colonization at the time of delivery (P = 0.20). Conclusion: A regimen of outpatient amoxicillin was associated with persistent GBS colonization in 43% of women at the time of labor. Oral prenatal antibiotic prophylaxis against GBS does not sufficiently reduce colonization to preclude intrapartum intravenous antibiotics.