Probiotics and Prebiotics in Fertility: Can the Gut Microbiome Improve Your Chances of Conceiving?

In recent years, the gut environment, or gut microbiome, has drawn a great deal of attention for its influence on how our bodies function as a whole. In reproductive medicine too, there is growing interest in the possibility that probiotics and prebiotics might play a role in the journey toward pregnancy. But how far has the science actually come?

Please note: much of what I describe in this article comes from basic research such as cell and animal studies. Effectiveness and effects in humans have not been established.

The Link Between the Gut Microbiome and Reproductive Function: Where the Research Stands

Our bodies live in partnership with an enormous number of bacteria. The gut in particular hosts a wide variety of species that together form a complex ecosystem. A hypothesis has been put forward that the balance of this gut microbiome influences ovarian function, implantation and the maintenance of pregnancy.

Let me place that clearly before going further. This is at the hypothesis stage, and no trial has shown that taking probiotics makes pregnancy more likely. What follows is the reasoning behind the idea, not a set of verified findings.

A useful comparison: research on bacteria inside the uterus has progressed somewhat further. In a pooled analysis of 12 studies and 2,154 patients looking at antibiotic treatment for chronic endometritis, there was no significant difference in ongoing pregnancy or live birth between those treated and those not treated (p = 0.09; PMID: 36405621). Even in an area where the intervention is studied directly, changing the bacterial state has not translated easily into better reproductive outcomes.

What Are Probiotics?

Probiotics are live microorganisms that, when taken in adequate amounts, confer a benefit on the host. The lactic acid bacteria and bifidobacteria found in yogurt and fermented milk drinks are the best-known examples. By supporting the gut environment, they are thought to contribute to better digestion and absorption and to the regulation of immune function.

What Are Prebiotics?

Prebiotics are non-digestible food components that specifically promote the growth or activity of particular beneficial gut bacteria and thereby have a favorable effect on the host's health. Oligosaccharides and dietary fiber fall into this category. They are understood to act as "food" that allows probiotics to do their work.

Potential Effects on Fertility

In animal models and in early-stage research, the gut environment has been reported as possibly related to reproductive function in the following ways.

Regulating hormone balance: It has been suggested that gut bacteria are involved in the metabolism of female hormones and may therefore potentially influence the regularity of ovulation and the menstrual cycle.
Suppressing inflammation: Chronic inflammation can be a contributor to infertility. The idea that improving the gut environment might dampen inflammatory responses and so benefit reproductive function is still at the stage of expectation, not proof.
Improving the endometrial environment: The uterus has its own microbiome, which may be connected to the gut environment. A healthy endometrium matters for embryo implantation.

That said, these findings remain possibilities. Large-scale clinical research in humans has not established their effectiveness, their safety, or the best way to take them. At present, firm evidence is lacking that any specific probiotic or prebiotic has a direct effect on reproductive function.

Limitations of the Research and What Lies Ahead

Research into how probiotics and prebiotics affect fertility is only at the beginning. It carries several limitations.

High heterogeneity: Study designs, participant characteristics, the bacterial strains and doses used, and the length of the intervention differ greatly from study to study, which makes consistent results hard to obtain.
Unclear mechanisms: The detailed pathways by which the gut might influence reproductive function have not yet been sufficiently worked out.
The need for individualized care: The gut microbiome varies widely between individuals, so something effective for one person may not be effective for another.

For now, I cannot actively recommend any particular probiotic or prebiotic as being "good for fertility." What I can say is that caring for the gut environment matters for general health, and it may indirectly support physical and mental wellbeing. A balanced diet, moderate exercise, and other basic improvements to daily life are a reasonable first step on a healthy path toward pregnancy.

For general information about the journey to pregnancy and about your own body, I invite you to look through the specialist perspectives on our home page. Information to support your day-to-day health is also available here.

Frequently Asked Questions (FAQ)

Q1: Is it safe to take probiotics or prebiotics during fertility treatment?

A1: Probiotics and prebiotics consumed as ordinary foods are generally considered to have a good safety profile. However, if you are undergoing fertility treatment and are considering them as a dedicated supplement, please always discuss it with your own doctor first. Depending on your health status and the treatment you are receiving, unexpected effects are possible.

Q2: Which foods contain probiotics and prebiotics?

A2: Probiotics are abundant in fermented foods such as yogurt, kefir, natto, miso, and pickled vegetables. Prebiotics are found in fiber-rich foods, including vegetables and fruits such as onions, burdock root, asparagus, and bananas, as well as seaweeds and mushrooms. Including these in your diet in a balanced way is likely to be helpful for general health.

Q3: Can looking after the gut environment also help reduce stress?

A3: The gut and the brain communicate closely, in what is known as the gut-brain axis. It has been suggested that supporting the gut environment influences the production of neurotransmitters and may have a favorable effect on mood and stress responses. Stress is something many women face while trying to conceive, and it is possible that gut care indirectly supports emotional wellbeing.

Summary

Research into the possible effects of probiotics, prebiotics, and the gut microbiome on reproductive function is very much ongoing. At this point, conclusive evidence about direct effects in humans and about the best way to take them is lacking, and no one can honestly claim that a particular product has a "dramatic effect" on fertility.

Even so, from the standpoint of general health, a balanced diet and a well-maintained gut environment are important. Stay attentive to your own body, and please bring any concerns to a specialist. Your feelings deserve to be respected. There is no need to rush: gather information at your own pace, and consider the best options together with a professional.

References

Antibiotic therapy for chronic endometritis and its reproductive outcomes: a systematic review and meta-analysis. Int J Fertil Steril. 2022. PMID: 36405621 (cited as a comparison; treated versus untreated showed no significant difference in ongoing pregnancy or live birth)

No trial was found testing whether probiotics or prebiotics affect reproductive outcomes in humans. We state that openly rather than filling the space with general references.

📖 A book by the same author covering the fundamentals of fertility and preconception care is available here: Amazon.co.jp