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

Objective: To determine the effects on the vaginal microbiota of an oral probiotic preparation administered from early pregnancy.

Design: Randomised, double blind, placebo-controlled trial.

Setting: Four maternity units in the UK.

Population: Women aged 16 years or older recruited at 9-14 weeks' gestation.

Methods: Participants were randomly allocated to receive oral capsules of probiotic containing Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 each at 2.5 × 10⁹ colony-forming units (CFUs) or placebo once daily from recruitment until the end of pregnancy.

Main outcome measure: Rates of bacterial vaginosis (BV, defined as Nugent score ≥7) at 18-20 weeks' gestation compared by logistic regression adjusted for possible confounders.

Results: The primary analysis included 78% (238/304) of participants who initially consented (probiotic group 123, placebo group 115). Of these participants, 95% (227/238) reported an intake of 93% or more of the required number of capsules. The rates of BV did not differ between groups at 18-20 weeks' gestation (15% (19/123) in the probiotic group vs. 9% (10/115) in the placebo group, adjusted odds ratio 1.82, 95% confidence interval 0.64-5.19). There were also no differences between the groups in the proportion of women colonised with the probiotic strains, Escherichia coli, group B streptococci or other vaginal microbiota. There were no differences in the alpha diversity or composition of the bacterial communities between or within the probiotic and placebo groups at 9-14 and 18-20 weeks' gestation.

Conclusions: Oral probiotics taken from early pregnancy did not modify the vaginal microbiota.

Tweetable abstract: The oral probiotic preparation used in this study does not prevent BV in pregnant women.