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.
What the research shows
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.
Best studied probiotic strains
CECT5713
Evidence is preliminary but high quality; strain-specific effect demonstrated.
Lactobacillus
Evidence supports use in male infertility; effects on female fertility less clear.
Who may benefit
Safety
No significant adverse events or increased miscarriage rates were reported in the reviewed studies. Probiotic supplementation appears generally safe in the studied populations.
Limitations
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.
PubMed sources
| Study | Type | Year | PMID |
|---|---|---|---|
| Time-to-conception and clinical pregnancy rate with a myo-inositol, probiotics, and micronutrient supplement: secondary outcomes of the NiPPeR randomized trial. Fertility and sterility |
Randomized Controlled Trial | 2023 | 36754158 |
| CECT5713 Increases Term Pregnancies in Women with Infertility of Unknown Origin: A Randomized, Triple-Blind, Placebo-Controlled Trial. Nutrients |
Randomized Controlled Trial | 2025 | 40507130 |
| Nutritional Intervention Preconception and During Pregnancy to Maintain Healthy Glucose Metabolism and Offspring Health ("NiPPeR"): study protocol for a randomised controlled trial. Trials |
Randomized Controlled Trial | 2017 | 28320484 |
| Efficacy and safety of nutritional supplements in female infertility: a network meta-analysis. Reproductive biology and endocrinology : RB&E |
Meta-analysis | 2025 | 41254684 |
| Probiotics supplementation in the treatment of male infertility: A Systematic Review. JBRA assisted reproduction |
Systematic Review | 2024 | 38530761 |
| Do probiotic interventions improve female unexplained infertility? A critical commentary. Reproductive biomedicine online |
Research Study | 2024 | 38359733 |
| Probiotic therapy in couples with infertility: A systematic review. European journal of obstetrics, gynecology, and reproductive biology |
Systematic Review | 2021 | 33188995 |
| A NEW APPROACH TO ASSISTED REPRODUCTIVE TECHNOLOGIES PREPARATION IN WOMEN WITH ENDOMETRIOSIS ASSOCIATED INFERTILITY USING PROBIOTICS. Polski merkuriusz lekarski : organ Polskiego Towarzystwa Lekarskiego |
Research Study | 2023 | 37589108 |
| The effect of vitamin D supplementation and vaginal probiotics on fertility in women with recurrent implantation failure: A randomized clinical trial. Human immunology |
Randomized Controlled Trial | 2025 | 39955996 |
| Dose-Dependent Effects of Probiotics on the Reproductive Performance, Egg Characteristics, and Seminal Traits of Broiler Breeders: A Model-Based Meta-Analysis. Journal of animal physiology and animal nutrition |
Meta-analysis | 2025 | 40323117 |