Oral Lactobacillus crispatus M247 Supplementation and Persistence of Vaginal Group B Streptococcus Colonization During Pregnancy

Background: Group B Streptococcus (GBS) colonization during pregnancy increases neonatal infection risk and is managed with intrapartum antibiotic prophylaxis. We evaluated whether oral probiotic supplementation was associated with reduced persistence of vaginal GBS colonization. Methods: This prospective, non-randomized, contemporaneous controlled intervention study included pregnant women with confirmed vaginal GBS colonization at 24–26 weeks of gestation. Participants selected either oral Lactobacillus crispatus M247 (20 billion colony-forming units (CFU) daily for eight weeks) or standard prenatal care. Vaginal cultures were repeated at 34–36 weeks. The primary outcome was persistent GBS colonization. Fisher’s exact test and relative risk (RR) were used. Exploratory Firth logistic regression adjusted for age, body mass index, and previous GBS colonization status; sensitivity analysis excluded unknown status. Trial registration: ISRCTN47071089, retrospectively registered. Results: Of 53 enrolled women (24 probiotic; 29 control), one control participant was lost to follow-up, leaving 52 for analysis. Persistent colonization was less frequent in the probiotic group than in controls (12.5% vs. 57.1%; p = 0.001; RR 0.219, 95% confidence interval (CI) 0.072–0.661). In the primary Firth model (n = 52; 19 events), probiotic use was associated with lower odds of persistence (adjusted odds ratio (aOR) 0.13, 95% CI 0.03–0.46; p = 0.001). Sensitivity analysis yielded similar results (n = 44; 15 events; aOR 0.17, 95% CI 0.03–0.63; p = 0.007). Self-reported adherence was complete, and no adverse events were reported among participants receiving the probiotic. Conclusions: Oral L. crispatus M247 supplementation from 24–26 weeks of gestation was associated with substantially lower persistence of vaginal GBS colonization in late pregnancy. Larger randomized controlled trials are required to confirm these findings.