Gut bacteria linked to fertility issues in women with polycystic ovary syndrome, research indicates

Women with polycystic ovary syndrome (PCOS) have lower levels of a gut microbe, new research suggests.

PCOS is the most common hormonal condition in women of reproductive age and yet, despite being a leading cause of infertility, very little is known about what causes it or how to treat it.

It can cause irregular or missed periods, excessive hair growth, weight gain and put women at higher risk for type 2 diabetes, high blood pressure, heart problems and endometrial cancer.

Aixia Liu at Zhejiang University in China and her colleagues monitored 220 women across 44 cities in China, half of whom had PCOS. All were under the age of 35 and provided samples of blood, stool and inner lining of their uterus.

Both those with PCOS and those without experienced similar pregnancy rates, yet the group with PCOS were twice as likely to experience complications, including miscarriage, preterm birth and gestational diabetes.

The research also found those with PCOS had around half the amount of a gut bacteria called Parabacteroides Merdae.

P Merdae helps convert a nutrient present in the gut called isoleucine into a healthy substance called short-chain fatty acids, which are good for reproductive health. Those with PCOS, had too much isoleucine in their blood and uterus because they had less of the gut bacteria to change into the helpful short-chain fatty acids.

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When scientists gave extra isoleucine to cells from the uterus, they also found it caused them to age and stop working properly.

This research suggested a lack of the P Merdae gut bacteria meant it was harder to get pregnant, because the excess isoleucine was damaging reproductive cells.

But while this may suggest changing the gut microbiome could improve fertility outcomes, some doctors are sceptical.

Andrea Dunaif, from the Icahn School of Medicine at Mount Sinai in New York, told the New Scientist her research suggested fertility often improved for women with PCOS in their 30s, rather than causing early ageing of the cells as this new research would suggest.

Yet, the findings may still lead to improved treatments for those with the condition.

"The microbiome is something [where] you could intervene with different probiotics to alter the [bacteria]," she said.

"So that is nice to have a potential target to treat because we don't really have any specific treatments for PCOS."

(c) Sky News 2025: Gut bacteria linked to fertility issues in women with polycystic ovary syndrome, research i