Vaginorectal colonization with Group B Streptococcus (GBS) has historically been associated with higher rates of chorioamnionitis and postpartum infection. Data from a recent observational cohort suggests a possible reversal of this association. In order to minimize confounding by differences in labor management, we sought to assess the association between GBS positivity and chorioamnionitis within the context of a randomized induction trial with a standardized labor protocol.
We performed a secondary analysis of a randomized trial of patients undergoing term induction at a tertiary care center. Patients received third trimester GBS screening and intrapartum antibiotic prophylaxis (IAP) per ACOG guidelines. Labor management was protocolized per the trial. Patients with unknown GBS status were excluded. The primary outcome was clinical diagnosis of chorioamnionitis, compared between GBS positive (by culture, history, or UTI) and GBS negative. Secondary outcomes included postpartum endometritis, wound infection, and a composite postpartum infectious morbidity.
A total of 491 patients were enrolled in the trial; 476 had a known GBS status and were included (292 (61.3%) GBS negative; 184 (38.7%) GBS positive), Table. The majority of patients were Black (77.9%) and nulliparous (59.2%). There were no differences in demographic, clinical, induction, or labor characteristics between groups. GBS positive patients were 52% less likely to be diagnosed with chorioamnionitis (8.1% vs. 14.7%, OR 0.52, p=0.03) or with any composite postpartum infectious morbidity (8.2% vs. 15.8%, OR 0.47, p=0.02) compared to GBS negative patients.
While GBS colonization has historically been considered a risk factor for maternal infection, our findings demonstrate that among patients undergoing induction with protocolized labor management, GBS positivity is associated with lower rates of chorioamnionitis and infectious morbidity, raising the possibility that IAP for GBS prophylaxis may protect against maternal infectious morbidity, a phenomenon that warrants further investigation.
© 2022 Published by Elsevier Inc.