Ask an Ob/Gyn: What causes PMOS?

Revisiting the research on what causes PMOS

This week we’re revisiting one of our most requested topics: what does the research say about how, exactly, polyendocrine metabolic ovarian syndrome (PMOS, formerly PCOS) develops? Unfortunately, we’ve yet to find the silver bullet that reveals the precise chain of events leading to the condition, but science has made real progress in recent years.

One thing before we dive in: in May 2026, PCOS was officially renamed polyendocrine metabolic ovarian syndrome, or PMOS, following a global consensus process led by researchers at Monash University and endorsed by the Endocrine Society and dozens of other organizations ¹. Diagnosis and treatment haven’t changed, only the name has. For the full story on why, check out our guide to PMOS, formerly known as PCOS. This article uses the updated name throughout.

In case you missed our last blog post or need a quick recap, find that article here. Meanwhile, here’s the TL;DR:

PMOS is an endocrine disorder, meaning it’s related to the endocrine system, the system responsible for the production and regulation of hormone levels. PMOS is a bit of a medical enigma because its causes are myriad, and it can present with varying symptoms, including cystic acne, missing or infrequent periods, heavy periods, unwanted body hair growth, polycystic ovaries, and insulin resistance.

PMOS is the main cause of anovulatory infertility, also known as infertility caused by lack of ovulation (the ovary doesn’t release eggs). It’s a fairly common condition, affecting an estimated 10 to 13 percent of AFAB individuals of reproductive age, or roughly 1 in 8, worldwide ². Besides the physical symptoms of PMOS, it is sometimes also associated with certain mental health disorders. A 2025 meta-analysis found that anxiety and depression symptoms are consistently and substantially more common in people with PMOS than in the general population ³, along with elevated rates of depression, bipolar disorder, and obsessive compulsive disorder ⁴.

So… do we know the exact cause of PMOS?

The exact cause, or causes, of PMOS remains unclear. This means there’s no one panacea to treat it.

What we do know is that many people with PMOS have insulin resistance. This may result in higher androgen levels, a key criterion for diagnosis. Medical research has also found that about half of those with PMOS are obese, and obesity is known to contribute to high levels of insulin, so the two conditions can have the effect of working synergistically and exacerbating symptoms. Lastly, some believe PMOS is mostly genetic ⁵.

At the end of the day, much research still needs to be conducted before we’ll know with certainty what exact chain of events must take place in the body to lead to PMOS.

PMOS causes, diagnosis, and management

While we don’t know the exact causes of PMOS, the condition is relatively straightforward when it comes to diagnosis. In most cases, a medical provider will review medical history, any presenting signs and common symptoms (like acne, unwanted or excessive hair growth), and perform a pelvic exam.

Aside from a physical exam, the doctor can also order an ultrasound to examine the size of the ovaries. Follicles identified with PMOS are typically not large; in fact, they often present as tiny fluid filled sacs (12 or more) located peripherally around the ovary, containing immature eggs ⁶. Blood tests are also used to check for high levels of a reproductive hormone called androgen and to evaluate blood glucose levels.

This is also part of why the condition’s name changed in 2026. The research behind the rename found no true increase in abnormal ovarian cysts among people with PMOS. What shows up on ultrasound is a higher number of small, immature egg follicles, not cysts in the medical sense ¹.

Androgens are hormones that play a role in the development of male traits, but they’re also present in females. In the context of PMOS, high levels of androgens can lead to symptoms such as acne and excess hair growth. These high levels are often associated with insulin resistance, which contributes to the hormonal imbalance seen in PMOS.

Managing this condition typically involves a combination of lifestyle changes, medication to regulate hormones and improve insulin sensitivity, and sometimes fertility treatments for those trying to conceive.

Importantly, it’s not necessary to have the characteristic follicle pattern on ultrasound in order to have a diagnosis of PMOS. As of the 2023 international guideline, a blood test measuring anti-Müllerian hormone (AMH) can also stand in for the ultrasound to confirm this finding ².

There are three different sets of criteria used for a PMOS diagnosis: the National Institutes of Health Criteria, the Rotterdam Criteria, and the Androgen Excess and PCOS Society Criteria. Usually, two out of three of the following equals a diagnosis:

1. Hyperandrogenism (a hormonal imbalance where high androgen levels are evidenced, for example, by cystic acne or unwanted hair growth, or as seen on bloodwork)
2. Oligomenorrhea (infrequent, irregular periods)
3. Polycystic ovaries, or elevated AMH

Because PMOS affects not only the reproductive organs but various organ systems, management of the condition is most effective when individualized and based on your unique symptoms and fertility goals. Some of the available treatment methods include lifestyle changes, hormonal birth control, laparoscopic ovarian drilling, or various oral medications.

In many cases, patients with PMOS will be prescribed more than one oral medication. For example, a birth control pill might be recommended to help with hormonal balance and to regulate your menstrual cycle, while spironolactone may be added to treat unwanted hair growth and hair loss as well as cystic acne (it does so by lowering androgen levels). For those with more significant insulin resistance, medications for diabetes, such as metformin, liraglutide, or dapagliflozin, may also be prescribed.

We asked Flex medical advisor Dr. Jane van Dis about what she recommends to patients diagnosed with PMOS:

“PMOS is a multifactorial disease and there isn’t a one size fits all recommendation for each patient,” she explains.

“Having said that, we know that exercise is one of the biggest components in reducing insulin resistance in PMOS. A meta-analysis of 16 studies showed that vigorous exercise was the most likely to reduce insulin resistance. For some women, PMOS is genetic, for others, it can be due to environmental exposures, but regardless, women shouldn’t feel helpless as there are medications that can be helpful, as well as exercise and nutrition components.”

What’s behind this tough to pinpoint syndrome? Research continues to look to insulin resistance, inflammation, and gut microbiota for answers. Some studies show promising findings regarding the connection between insulin resistance and the gut microbiome, which is responsible for a diverse range of 1,000 to 1,500 species of bacteria.

Let’s take a closer look at these potential PMOS causes.

Insulin resistance and the gut

A study published in the Journal of Ovarian Research showed that gut microbiota composition in patients with PMOS was significantly different compared with those without ⁷.

This study also points out the important link between intestinal flora and factors like obesity and insulin resistance, noting that about half of patients with PMOS are insulin resistant. Insulin is a hormone that regulates blood sugar levels by facilitating the uptake of glucose from the bloodstream into cells. In addition to body weight gain and high blood pressure, among other signs, insulin resistance also plays a role in excess androgen production, leading to hirsutism, acne, and maybe even the development of follicles in the ovary ⁸.

As the researchers note, “Insulin resistance is also associated with endotoxemia, chronic inflammatory response, short-chain fatty acids, and bile acid metabolism.” In other words, insulin resistance and chronic inflammation are closely connected ⁸.

The study goes on to state, “When intestinal barrier function is impaired, endotoxin produced by intestinal flora enters the blood, causing chronic ovarian inflammation and insulin resistance, hence promoting the occurrence and development of PMOS” ⁸.

The authors point to other research confirming that intestinal flora can regulate the secretion of insulin, resulting in affected androgen metabolism and the development of follicles. Because of this link, the authors call on future studies to look at bacterial profiles and the manipulation of intestinal microbiota as possible treatments. A more recent 2025 review reinforces this, noting that gut microbiota dysbiosis may promote insulin resistance, disrupted glucose metabolism, and lipid imbalances in PMOS, and points to short-chain fatty acids as a promising treatment target ⁹.

The gut microbiota governs many aspects of health, from metabolism and immunity to pathogen prevention. So, in some ways, it’s not surprising that it might also influence reproductive health.

Another study by the Endocrine Society looked at two groups of obese teenagers, one group with PMOS and one without. All participants had similar BMIs ¹⁰. The study found that the microbiota was significantly altered in adolescents with PMOS, as opposed to adolescents without the condition. These findings show just how important a role gut microbiota play in metabolic disease in adolescents, and perhaps all individuals, with PMOS.

The same study also examined the correlation between insulin levels and inflammatory response. A state of chronic inflammation affects multiple organs, and particularly affects the insulin receptor and even follicle development.

The authors note, “A leaky gut has been hypothesized to mediate the development of the metabolic syndrome via upregulation of systemic inflammatory response. The systemic inflammatory response has been shown to disrupt various organ functions and could contribute to insulin resistance” ¹¹.

To further examine the relationship between microbiota and PMOS, let’s take a look at a third study that examined a group of rats induced with the condition ¹². The animals displayed similar symptoms to humans with PMOS: irregular menstrual periods, increasing androgens, and cysts in ovarian tissue.

The rats were treated with fecal microbiota transplantation (FMT) and Lactobacillus, a healthy bacterium that lives in the intestinal tract. The results? Menstrual cycles improved in all treated rats, and six of the eight rats in the Lactobacillus transplantation group showed decreasing androgen production.

This indicates that an imbalance of gut microbiota is associated with the development of PMOS, and that we might benefit from keeping gut considerations front of mind for treatment. To summarize, as concluded by the authors of the first study we mentioned, “Accumulating evidence has recommended probiotics, prebiotics, synbiotics as effective treatment options for PCOS patients” ⁸.

Curious about whether probiotics or prebiotics could help your PMOS? It’s always a good idea to consult with your doctor before adding anything new to your diet or supplement regimen, but the research looks promising.

Inflammation and PMOS

As with a range of other conditions, researchers have found a strong link between PMOS and inflammatory markers. One study examined 200 people ages 18 to 40 with PMOS compared to a healthy control group of 105 people, looking at white blood cell counts and C-reactive protein (CRP) concentration ¹³.

The study concluded that white blood cell counts were significantly higher in PMOS patients. Insulin, glucose, and cholesterol were also elevated. The findings of both increased white blood cells and CRP suggest that chronic low grade inflammation is present in PMOS ¹⁴.

New lifestyle recommendations for PMOS

Because there is still no cure all treatment for PMOS, it’s important to factor in all of the presenting symptoms when coming up with a treatment plan. Work closely with your healthcare provider or, better yet, reach out to a specialist.

If possible, equip yourself with a multidisciplinary team of providers, for example, a gynecologist, endocrinologist, dermatologist, and dietician, in addition to a primary care physician. Having multiple specialists on board will allow you to tackle PMOS, its symptoms, and its root causes from all angles.

As we mentioned earlier, PMOS left untreated can lead to serious health problems and complications down the road, including, but not limited to, infertility. Dr. Jane adds, “Women with excess levels of estrogen are at increased risk of breast and uterine cancer, and women with excess testosterone are at increased risk of cardiovascular disease. Both can be deadly, which is why, if you have PMOS, it’s really important to treat it aggressively and watch for any abnormal uterine bleeding.”

This is not to say that a PMOS diagnosis is necessarily life threatening. Rather, it’s important that you work closely with your healthcare provider to monitor your symptoms and come up with a treatment plan.

Balancing diet and exercise

It’s helpful to remember that insulin resistance can be managed with proper nutrition, especially a diet high in fiber and low in refined sugar. Obesity complicates PMOS, and insulin resistance typically makes losing weight more difficult. That’s where the other piece of the puzzle comes into play: Nicholas D. Carricato, MD, says that “moderate exercise can help make your body more sensitive to insulin” and may help with weight loss and symptom management as well ¹⁵.

Official guidelines for PMOS management recommend at least 150 minutes of physical activity per week ¹⁶. This breaks down to only about 21 minutes per day which, thankfully, is totally doable. Find something you enjoy doing, whether that’s a team sport, a swim club, or even a local hiking group, to make your workouts feel more like an activity to look forward to and less like a chore.

Dr. Jane recommends adjusting both your diet and exercise routine to maximize the benefits of both: “Diet is always the most important for weight loss,” she notes. “That said, building up muscle mass, like with weight training, is a great way to build exercise endurance, along with increasing baseline metabolism. Cardiovascular exercise is great for heart and vascular health. So, in reality, you shouldn’t leave diet or exercise out.”

For inflammation, “a low carbohydrate diet will help increase production of short chain fatty acids which reduces incidence of chronic inflammation” ⁸.

Other research suggests that high sugar foods may be one of the inducers of PMOS, the reasoning being that they tend to cause intestinal flora imbalance and trigger chronic inflammation, insulin resistance, and production of androgens. With that in mind, try your best to minimize sugary foods in your diet and look for healthier alternatives to things like soda, candy, and baked goods.

Some of our favorite swaps include:

• Soda → Flavored sparkling water
• Candy → Dark chocolate covered strawberries
• Baked goods → Oatmeal with sliced apples and almond butter
• Ice cream → Homemade chocolate “nice cream” made with (yes, really) avocados
• Fruit juice → Unsweetened iced tea
• Sugary “low fat” yogurt → Plain Greek yogurt with fresh berries

We know, easier said than done, especially when you’re on your period. Working with a dietician or nutritionist will help you find even more healthy swaps so you can improve your eating habits without feeling deprived on your journey to achieving and keeping a healthy weight.

If cost is a limiting factor, keep in mind some nutrition counselors accept sliding scale payment, and there are great online communities where you can find helpful tips and support free of charge. Certain health insurance plans will cover nutritionist or dietician services as well.

How does PMOS affect pregnancy?

PMOS can lead to infertility, making it harder to conceive. It increases the risk of pregnancy complications, such as gestational diabetes and preeclampsia ². Women with PMOS may also have a higher risk of miscarriage and premature birth, requiring careful monitoring and management during pregnancy.

Although one of the most common causes of infertility, women with PMOS can still experience successful pregnancies with proper medical guidance and support. It’s essential for women with PMOS to work closely with healthcare providers to manage their condition and maximize their chances of a healthy pregnancy. This may involve lifestyle adjustments, medication management, and monitoring throughout the pregnancy journey.

Here are some other excellent resources for PMOS:

• @the.hormone.dietician on Instagram
• The PCOS Awareness Association
• The National Polycystic Ovary Syndrome Association
• Information on PCOS from ACOG
• Verity PCOS Self-Help Group
• r/PCOS on Reddit

This article is informational only and is not offered as medical advice, nor does it substitute for a consultation with your physician. If you have any gynecological/medical concerns or conditions, please consult your physician. 

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