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Probiotics in late pregnancy may not reduce GBS colonization but can beneficially shift vaginal microbiota composition. 

Researchers conducted a retrospective study published in the June 2025 issue of European Journal of Obstetrics and Gynecology and Reproductive Biology to evaluate the feasibility and effects of using probiotics in pregnancy, beginning in the third trimester, on rectovaginal colonization of group B streptococcus (GBS) in women at low obstetric risk.  

They performed a study in 3 tertiary hospitals in northern Italy involving low-risk pregnant women. From 30 to 37 weeks of pregnancy, participants received either 2 capsules of probiotics or a placebo daily. The primary outcome, GBS colonization, was assessed using rectovaginal swabs. In a randomly selected subgroup, changes in the vaginal microbiome were evaluated with 16S Metagenomic Sequencing Library Preparation sequencing and analysis.  

The results showed no significant difference in rectovaginal swab positivity (P = 0.24) and antibiotic use (P = 0.27) between the probiotics (n = 133) and placebo (n = 134) groups, 1 postpartum fever case (>38 °C) occurred in the placebo group. Labor, delivery, and neonatal outcomes were comparable in both groups. Vaginal microbiota analysis revealed no significant change in Lactobacillus spp. abundance, but Gardnerella spp. decreased significantly (3.6 ± 7.9 vs 5.5 ± 10.2; P = 0.03). The Lactobacillus spp. levels significantly decreased in women with partial rupture of membranes (46.9 ± 43.6 vs 77.7 ± 24.9; P = 0.02).  

Investigators concluded that although clinical outcomes had remained unaffected, the administration of probiotics had led to favourable changes in vaginal microbiota. 

Source: ejog.org/article/S0301-2115(25)00245-3/fulltext