The Gut microbiome
The gut microbiome plays a crucial role in our overall health, with the majority of our body’s microbes residing in the gut. Interestingly, about 9% of a woman’s microbial population is found in the reproductive tract.
The gut microbiota, which includes trillions of microorganisms, has a significant impact on the endocrine reproductive system by interacting with key hormones such as oestrogen, androgens, and insulin. This interaction suggests that the gut microbiome may be involved in conditions like Polycystic Ovary Syndrome (PCOS) and endometriosis, both of which are risk factors for infertility.
Moreover, research indicates that gut dysbiosis—a shift in the gut microbiota from a healthy state to one associated with disease—can lead to inflammation and immune dysregulation, further influencing reproductive health. Although some studies have found differences in the gut microbiome between fertile and infertile women, a direct causal link between dysbiosis and infertility has not yet been established.
The Vaginal microbiome
The vaginal microbiome is another critical factor in reproductive health, with Lactobacillus being one of the predominant bacteria in the vaginal environment of healthy women. Lactobacillus produces lactic acid, which helps prevent the overgrowth of potentially harmful yeast, bacteria, and viruses. Research suggests that when the vaginal microbiome is not dominated by Lactobacillus, it may lead to dysbiosis, which has been linked to implantation failure and lower pregnancy rates in IVF, although it does not appear to affect live birth rates.
A healthy vaginal microbiota is also associated with a lower risk of miscarriage. In fact, low levels of Lactobacillus have been linked to early miscarriage and implantation failure. Additionally, vaginal dysbiosis has been correlated with pregnancy complications such as preterm birth.
The Endometrial microbiome
The endometrial microbiome, a relatively recent area of research, is gaining attention for its potential impact on reproductive health. The endometrium was traditionally considered a sterile environment. However, it is now known that it hosts a unique microbial community that may play a significant role in fertility and reproductive outcomes.
The endometrial microbiome is typically less diverse than the gut or vaginal microbiomes, with Lactobacillus species often dominating a healthy endometrial environment. The presence of a Lactobacillus-dominant microbiome in the endometrium is associated with favourable reproductive outcomes, including higher implantation rates and successful pregnancies in women undergoing assisted reproductive technologies (ART) such as IVF.
Conversely, an imbalance in the endometrial microbiome, known as dysbiosis, has been linked to various reproductive challenges such as endometritis, implantation failure and recurrent miscarriage.
Both the gut and vaginal microbiomes may play a role in conditions like PCOS and endometriosis. Research has found lower levels of beneficial Lactobacillus in individuals with these conditions, suggesting a potential link between microbiome health and reproductive outcomes. There is also emerging evidence exploring the associations between the endometrial microbiome and PCOS and endometriosis but more research is required.
Can probiotics help?
The potential of probiotics to improve reproductive outcomes is an area of active research, though still in its early stages. Emerging studies show promising results. For example, intravaginal probiotics containing Lactobacillus may support fertility and could potentially increase live birth rates in women with bacterial vaginosis. These probiotics might influence the endometrial microbiome and could also reduce miscarriage rates.
Oral probiotics, particularly those containing Lactobacillus, may improve live birth rates in individuals with a history of recurrent miscarriage. However, evidence on the efficacy of probiotic therapy for women undergoing assisted reproduction is conflicting, and more high-quality randomised controlled trials are needed.
In the context of PCOS and endometriosis, early research suggests that Lactobacillus probiotics could be beneficial as low levels of Lactobacillus are indicated in both conditions, though more studies are required to confirm these findings.
How to keep a healthy gut microbiome through diet
Diet plays a vital role in maintaining a healthy gut microbiome. Consuming live dietary microbes found in foods like kefir or yoghurt can support gut health. Additionally, as seen above, considering a Lactobacillus-dominant probiotic may be beneficial.
A diet that supports gut microbiota diversity is also recommended. Such a diet is typically rich in fibre and includes whole grains, fruits, vegetables, nuts, seeds, legumes, and pulses. A Mediterranean-style diet, which features legumes, whole grains, nuts, seeds, lean meats, oily fish, and extra virgin olive oil, has been shown to support gut microbiome health.
Microbiome tests
Currently, the British Dietetic Association does not support the use of commercial microbiome tests due to the infancy of research in this area. Interpreting microbiome test results is challenging because there are no standardised reference values for what constitutes a “healthy” microbiome. While a healthy microbiome is generally described as diverse, resilient, and stable, this varies greatly between individuals and populations, making it difficult to apply these results to clinical decisions.
Some fertility clinics offer microbiome testing as an add-on to fertility treatments. If you are considering these tests, it is advisable to discuss them with your fertility specialist to determine whether they are relevant for your situation.
While microbiome tests may hold potential and, in some cases, provide useful information for fertility treatments, further randomised controlled trials are necessary to determine their effectiveness. Additionally, the cost of these tests is often high, so it is important to weigh the potential benefits against the expense. As research in this field continues to evolve, we may gain a clearer understanding of the role the microbiome plays in fertility and how we can best support it through diet, probiotics, and other interventions.
The bottom line
The microbiome’s role in reproductive health is becoming clearer, with the gut, vaginal, and endometrial microbiomes all appearing to influence fertility. While probiotics, particularly Lactobacillus, show promise in improving reproductive outcomes, more research is needed, especially for conditions like PCOS and endometriosis.
Maintaining a healthy microbiome through diet should be our first-line approach, but in the right patient, we may also consider Lactobacillus supplements. The use of commercial microbiome tests is still controversial due to limited evidence; while we can support patients interested in these tests, some patients may wish to trial a probiotic without pursuing a microbiome test for a more cost-effective, low-risk option.
The microbiome is a fascinating and emerging area of fertility care and we await more studies to better understand assessments, their interpretation, and the most effective treatment; but, it makes sense to start to pay attention to this area to ensure a holistic approach to fertility care.