It’s well known that polycystic ovary syndrome (PCOS) is a leading cause of infertility, but it’s not often discussed that PCOS is also tied to pregnancy complications, including miscarriage. A 2025 study seeking to better understand the underlying cause for this connection may have found an answer in the distinctive gut microbiomes of women with PCOS.
Patterns detected in gut microbiomes of participants with PCOS
The 2025 study, conducted in China, followed 220 women under the age of 35, half of whom had PCOS [1]. According to the press release for the study, the results revealed a pattern in the gut microbiomes of women with PCOS compared to those without. Specifically, “results showed a significant reduction in microbial diversity among PCOS patients, particularly a decrease in P. merdae.” Notably, P. merdae is a strain of beneficial bacteria that has been linked to metabolic health.
In addition, the press release notes that study participants with PCOS had higher levels of a branched-chain amino acid (BCAA) called isoleucine. This type of protein is referred to as “nutritionally essential,” meaning that it is only derived from food. (Food sources of isoleucine include animal products such as beef, chicken, pork, fish and dairy, as well as plant products like tofu, beans, lentils, whole grains, nuts, seeds, and some vegetables like peas.)
While women in the study with this distinctive pattern of gut microbiota reportedly achieved pregnancy at a similar rate to the control group, they were nearly twice as likely to experience at least one complication, including “miscarriage, preterm birth, macrosomia, low birth weight, gestational diabetes, hypertensive disorders, and perinatal death.”
Effects on the uterus
The press release further reports that researchers also found elevated levels of isoleucine in the endometrial cells of the study participants with PCOS. Further testing revealed that isoleucine inhibits the uterine lining from adapting to support a baby’s growth in the womb during pregnancy.
In fact, the researchers noted that endometrial cells exposed to high levels of isoleucine showed signs similar to aging, even though all of the women included in the study were under 35 years old. Thus, researchers suggest that the gut microbiome profile associated with PCOS might be compromising endometrial health, contributing to the higher rate of pregnancy complications.
Researchers suggest that the gut microbiome profile associated with PCOS might be compromising endometrial health, contributing to the higher rate of pregnancy complications.
PCOS and gut health
In the press release, Dr. Aixia Liu, the researcher who led the study, noted, “Many of these women [with PCOS] also had metabolic imbalances and digestive issues, which led us to explore the possible interplay between the gut microbiota, circulating metabolites, and the uterus.”
This study joins a growing body of evidence linking gut health to PCOS. Prior research has also found that women with PCOS have a less diversified gut microbiome. Both imbalances in the gut microbiome (also known as dysbiosis) and PCOS are tied to inflammation and metabolic issues like insulin resistance. It’s still not clear which causes which though: hormonal changes associated with PCOS have been found to alter the gut microbiome, and dysbiosis can cause PCOS-like symptoms.
Both conditions are increasingly widespread–up to 13% of women have PCOS, and gut imbalances are even more common. According to integrative women’s health specialist Dr. Aviva Romm, the majority of Americans suffer from dysbiosis, “as a result of years or decades of antibiotic overuse, a standard western diet practically devoid of healthy fibers, diets high in sugar, stress, and even endocrine disrupting chemicals that have been found, beyond a shadow of a doubt, to unfavorably alter our intestinal ecosystems.”
A vicious cycle–and a silver lining
This research, then, sheds new light on the multi-faceted issue of gut health, PCOS, infertility, and pregnancy complications.
Because PCOS is poorly understood, can manifest in many ways, and lacks a one-size-fits-all treatment, women often struggle with their symptoms for years without solutions or even a diagnosis. The prospect of a prematurely aging uterus triggered by gut dysbiosis might feel like an added weight to an already crushing set of health problems.
But the interconnected nature of these issues works both ways: as research continues to uncover the myriad ways that the gut microbiome is connected to fertility health, it offers women a path forward to heal multiple areas at once. In fact, treating gut dysbiosis has already been shown to mitigate PCOS symptoms [2]. Now, understanding how patterns in the gut can alter cells in the endometrium may lead to more targeted treatment for women who are struggling with infertility or at risk for miscarriage.
As research continues to uncover the myriad ways that the gut microbiome is connected to fertility health, it offers women a path forward to heal multiple areas at once. In fact, treating gut dysbiosis has already been shown to mitigate PCOS symptoms. Now, understanding how patterns in the gut can alter cells in the endometrium may lead to more targeted treatment for women who are struggling with infertility or at risk for miscarriage.
A step in the right direction
The researchers suggested that, based on the results of this study, low levels of P. merdae and high levels of isoleucine in the gut may be considered biomarkers, which could be used to identify women at high risk for pregnancy complications. As Dr. Liu remarked in the press release, “The next step is to explore whether dietary interventions, probiotics, or BCAA-restricted diets can reverse these effects and improve pregnancy outcomes.”
Hopefully, the effects on endometrial cells that Dr. Liu’s team observed also prove to be reversible. Regardless, her conclusions are heartening, as they express a desire to identify and treat root causes of infertility. Too often, PCOS symptoms are addressed with band-aid measures like hormonal birth contraceptives that don’t actually address the underlying issues (and which further contribute to poor gut health [3]!), and women who face infertility and pregnancy complications feel alone or—even worse—that they are to blame.
Too often, PCOS symptoms are addressed with band-aid measures like hormonal birth contraceptives that don’t actually address the underlying issues (and which further contribute to poor gut health!), and women who face infertility and pregnancy complications feel alone or—even worse—that they are to blame.
The bottom line: listen to your gut!
The evidence continues to confirm that gut health has a major influence on fertility health and pregnancy outcomes—for men and women, and for better or for worse. For some women, healing PCOS and preventing pregnancy complications may begin with restoring and supporting a healthy gut.
The 2025 Chinese study was only one small study, so its findings will need to be corroborated by more research. Nevertheless, it provides insight into an underlying cause for both PCOS and pregnancy complications, and in so doing points towards promising developments in a more holistic approach to women’s health.
