Effects of oral probiotic supplements on vaginal microbiota during pregnancy: a randomised, double‐blind, placebo‐controlled trial with microbiome analysis

Randomized, double-blind, placebo-controlled trial with vaginal microbiome analysis in pregnant women enrolled at 9 to 14 weeks' gestation. In the probiotic arm, 152 participants were randomized and 123 were included in the primary analysis; participants were recruited from four maternity units in East London, United Kingdom.

Oral probiotic capsules containing Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14, 2.5 billion CFUs of each strain per capsule, were taken once daily from recruitment until delivery. The capsules were matched to placebo aside from the probiotic strains.

Oral probiotic supplementation from early pregnancy did not meaningfully change vaginal microbiota or bacterial vaginosis outcomes. At 18 to 20 weeks' gestation, bacterial vaginosis occurred in 15% (19/123) of the probiotic group versus 9% (10/115) of placebo, with an adjusted OR of 1.82 (95% CI 0.64-5.19; P = 0.26). Vaginal colonization by L. rhamnosus GR-1 was only 5% (6/123) in the probiotic arm and 5% (6/115) in placebo, while L. reuteri RC-14 was not detected in either group. Alpha diversity and community composition did not differ significantly, and no serious adverse events related to the intervention were reported.

The primary analysis included fewer participants than were randomized in the probiotic arm, and the intervention showed very low vaginal colonization, limiting biological signal detection. Outcomes were largely microbiological with low event rates, and the study population was drawn from a single geographic region, which may limit generalizability.