Impact of microbiota on reproductive health

Infertility, whether affecting males or females, is a major global health concern, with an estimated prevalence of 8 to 12% of the population. Research ¹ on microbiota has provided new insights into reproductive health by identifying microbial communities that interact with the host at the metabolic, immune, and endocrine levels.

Key role of microbiota in the reproductive systems

In women, a vaginal microbiota dominated by Lactobacillus (particularly L. crispatus) is associated with an acidic pH, reduced inflammation, and an endometrium conducive to embryo implantation. Conversely, vaginal dysbiosis is associated with an elevated pH, increased production of pro-inflammatory metabolites, and impaired sperm motility, embryo implantation, and maternal-fetal immune tolerance. The endometrium is also thought to host a low-biomass microbiota. The presence of Lactobacillus is associated with improved reproductive outcomes (conception, implantation, clinical pregnancy, or live births), whereas Atopobium or Gardnerella are more frequently associated with failure.

In men, the seminal microbiota influences sperm quality: Lactobacillus is associated with lower production of oxidative compounds and better sperm DNA integrity, whereas Prevotella and Streptococcus are associated with inflammation and impaired sperm motility. However, evidence linking the seminal microbiota to male infertility is still emerging, as findings are often limited by small sample sizes and substantial inter-individual variability.

The gut microbiota is also involved

The gut microbiota may also influence fertility through immune, endocrine, and metabolic pathways. For example, in polyendocrine ovarian metabolic syndrome (formerly polycystic ovary syndrome), gut dysbiosis (characterized by reduced microbial diversity, increased Escherichia, decreased Lactobacillus) appears to promote inflammation, insulin resistance, and hormonal imbalances through the translocation of lipopolysaccharides (LPS) across the intestinal barrier and the disruption of intestinal enzymes. 

What mechanisms and interventions are involved?

The vaginal, uterine, intestinal, and seminal microbiota are thought to influence fertility through immuno-inflammatory and endocrine-metabolic mechanisms, as well as by maintaining a protective barrier effect.
Several approaches are being investigated to optimize microbiota prior to assisted reproductive technology (ART) treatments:

• antibiotics are effective for treating confirmed infections (chronic endometritis, vaginosis); some studies have reported improved clinical pregnancy rates following antibiotic treatment – sometimes doubling pregnancy rates in IVF – but antibiotic therapy also depletes beneficial Lactobacillus ;
• probiotics (oral or intravaginal) can partially restore microbial balance, although their effects on pregnancy outcomes remain inconsistent ;
• emerging therapies (fecal or vaginal transplantation) are promising but remain experimental and require well-controlled clinical trials.

Microbiota profiling could therefore become a valuable component of ART protocols by refining patient stratification and guiding targeted adjuvant therapies. However, before implementation, stronger causal evidence, validated biomarkers, and standardized methodological frameworks are required.