Altered gut microbiome linked to fertility issues in people with PCOS
People with PCOS who struggle to conceive tend to have lower levels of a gut microbe that has been linked to endometrial function
By Grace Wade
29 June 2025
Restoring levels of specific gut microbes might help treat fertility issues in people with PCOS
Science Photo Library / Alamy Stock Photo
Women with polycystic ovary syndrome (PCOS) have lower levels of a gut microbe, which appears to raise the risk of pregnancy complications.
PCOS is the most common hormonal condition in women of reproductive age and is a leading cause of infertility. Yet relatively little is understood about what causes it or how to best treat it. For instance, it isn’t clear why those with PCOS who are able to get pregnant have a higher risk of complications like miscarriage, preterm birth and gestational diabetes.
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Aixia Liu at Zhejiang University in China and her colleagues monitored pregnancy outcomes in 220 women across 44 cities in China, half of whom had PCOS. All of them were under 35 years old and provided blood, stool and tissues samples of their endometrium, or the inner lining of the uterus.
Despite similar pregnancy rates, those with PCOS were nearly twice as likely to experience a pregnancy complication, such as miscarriage, preterm birth, gestational diabetes or a child with low birth weight. The researchers also found that those with PCOS had about half the amount of a gut bacterium called Parabacteroides merdae than those without the condition and that this was associated with pregnancy outcomes.
P. merdae helps convert certain nutrients, such as the amino acid isoleucine, into beneficial compounds called short-chain fatty acids that play an important role in reproductive health. This probably explain why participants with PCOS had, on average, about 39 per cent more isoleucine and 10 per cent lower levels of short-chain fatty acids in blood samples than those without it. They also had higher levels of isoleucine in endometrial tissues.
