Lactobacillus-containing probiotics and clinical pregnancy in infertile women undergoing ART: a systematic review and meta-analysis

Abstract Objective To assess whether Lactobacillus-containing probiotics improve clinical pregnancy in infertile women undergoing assisted reproductive technology (ART). Methods We conducted a systematic review and meta-analysis (PROSPERO CRD420251149619). PubMed, Embase, and Web of Science were searched from Jan 1, 2005, to Oct 31, 2025 for full-text randomised controlled trials (RCTs) in infertile adult women undergoing ART that compared Lactobacillus-containing probiotics (vaginal or oral) with placebo or no supplementation before standard ART care. Two reviewers independently screened records, extracted published study-level data, and assessed risk of bias using RoB 2. We pooled risk ratios (RRs) using random-effects models (restricted maximum likelihood with Hartung–Knapp adjustment) and quantified heterogeneity with I². Results Seven RCTs (796 women; 399 probiotics, 397 control) were included. Probiotics were associated with higher clinical pregnancy than control (RR 1.49, 95% CI 1.07–2.07; I² = 29%). In absolute terms, the pooled risk difference was 0·124 (95% CI 0·014–0·234), corresponding to approximately 12·4 additional clinical pregnancies per 100 women treated. The 95% prediction interval was 0·76–2·94. Effects were larger with treatment duration > 14 days (RR 1.99, 95% CI 1.44–2.75; I² = 0%) than with ≤ 14 days (RR 1.16, 95% CI 0.67–2.00). Six trials were judged to be at low risk of bias and one was judged to have some concerns; adverse events were not reported in any included trial. Conclusion Lactobacillus-containing probiotics may be associated with improved clinical pregnancy in women undergoing ART, particularly in trials using courses longer than two weeks. Larger, well-blinded multicentre RCTs evaluating live birth are needed to standardise clinically meaningful probiotic regimens and assess safety.