Certain probiotic strains, particularly Lactobacillus and the strain CECT5713, show potential benefits for fertility, especially in cases of unexplained infertility and male infertility. Evidence for other strains or combinations is limited or mixed.
High-quality randomized controlled trials and systematic reviews indicate that oral administration of the probiotic strain CECT5713 significantly increased pregnancy success rates in couples with unexplained infertility. Lactobacillus strains have shown promise in improving sperm quality and motility in men with idiopathic infertility. A combination of vaginal probiotics and vitamin D supplementation improved pregnancy rates in women with recurrent implantation failure by modulating immune responses. However, evidence for probiotics improving female fertility outcomes is mixed, with some studies showing no significant benefit and others suggesting potential effects when combined with other supplements. Multistrain probiotics, including Bacillus subtilis, improved reproductive parameters in poultry models, but direct human evidence is lacking. Overall, strain-specific effects are important, and more high-quality research is needed to confirm benefits and identify optimal strains and formulations.
Evidence is preliminary but high quality; strain-specific effect demonstrated.
Evidence supports use in male infertility; effects on female fertility less clear.
No significant adverse events or increased miscarriage rates were reported in the reviewed studies. Probiotic supplementation appears generally safe in the studied populations.
Many studies combine probiotics with other supplements, making it difficult to isolate probiotic effects. Some evidence is preliminary or low certainty. Strain-specific effects limit generalizability. More large-scale, high-quality RCTs are needed, especially for female infertility. Variability in probiotic strains, dosages, and administration routes complicates conclusions.