Vaginal group B streptococcus status during intrapartum antibiotic prophylaxis

Abstract Objective To assess maternal group B streptococcus (GBS) colonization status and the pharmacokinetic profile of penicillin G in the umbilical cord and amniotic fluid compartment during 4 hours of intrapartum antibiotic prophylaxis (IAP). Methods In a prospective study at a hospital in Montevideo, Uruguay, 60 GBS carriers in active labor after a singleton pregnancy of 37 weeks or more were enrolled between April 1, 2011, and April 30, 2012. Intravenous penicillin G was administered via a standard regimen. Rectovaginal samples were obtained before IAP initiation, and 2 and 4 hours after the initial dose. Penicillin G concentrations were measured by high-performance liquid chromatography. Samples were obtained from fetal cord blood in all cases and from amniotic fluid obtained from patients who delivered by cesarean. Results Among the 60 participants, 43 (72%) had a positive rectovaginal sample before IAP initiation. Of these women, 23 (53%) had negative cultures after 2 hours; after 4 hours, only 5 (12%) remained positive for GBS. The penicillin G concentration in amniotic fluid and cord blood was above the minimum inhibitory concentration (0.12 μg/mL) in all cases. Conclusion Four hours of IAP was needed to reduce the number of women with positive GBS cultures to 12%. Therefore, 4 hours of IAP might be necessary to achieve overall effectiveness from this treatment.