The hidden connection: how your microbiome impacts fertility

Infertility affects approximately 1 in 10 couples. But a new discovery ¹ could bring them hope: the tiny bacteria that live in our bodies may play a key role in our ability to conceive. These communities interact with our immune system, our hormones, and our metabolism.

For women and men: a matter of balance

In women, a healthy vaginal microbiota is dominated by beneficial bacteria called Lactobacillus, particularly the species L. crispatus. These bacteria are allies of our intimate health by maintaining an acidic environment, limiting inflammation, and promoting the uterus’s receptivity to pregnancy. When this balance is disrupted (vaginal dysbiosis), other bacteria associated with an imbalance become more abundant: the vaginal pH rises, inflammation increases, potentially impairing sperm motility, embryo implantation and immune tolerance between the mother and the fetus.

The uterus is also believed to have its own microbiota. The presence of beneficial bacteria in the endometrium is thought to improve pregnancy rates, while certain pathogens are thought to reduce them. However, these findings remain controversial, because the samples are difficult to analyze and are highly susceptible to contamination.

In men, semen also contains its own microbiota. When beneficial bacteria dominate, they produce fewer inflammatory compounds and protect spermatic DNA. Conversely, certain pathogenic bacteria may increase inflammation and slow sperm motility. However, studies linking seminal microbiota to male fertility are still limited and require further research.

The gut: the hidden conductor?

The gut microbiota may also influence fertility through the immune system, hormones, and metabolism. In women with polyendocrine ovarian metabolic syndrome (formerly polycystic ovary syndrome), an imbalance in the gut microbiota seems to promote inflammation, insulin resistance, and hormonal disruptions. Another example is endometriosis, a condition associated with gut dysbiosis that may also alter estrogen metabolism, enhance inflammation, and contribute to the growth of lesions which could potentially affect the embryo’s ability to implant in the uterus.

How can balance be restored?

As a preventive measure, it is important to avoid any practices that may disrupt your vaginal or seminal microbiota and your gut microbiota. In the event of a confirmed bacterial infection (vaginosis), your doctor may prescribe appropriate treatment.
Approaches aimed at modulating microbiota to restore balance – such as probiotics – are also being investigated, but their impact on pregnancy outcomes remain uncertain. As for microbiota transplantations, they are still limited to clinical research. In the future, microbiota profiling could help better personalize care for couples undergoing assisted reproductive technology (ART) cycles. However, this approach remains under evaluation and requires more robust scientific evidence before it can be incorporated into standard clinical practice.