Women diagnosed with polycystic ovarian syndrome (PCOS) seem to face a heightened risk of pregnancy complications linked to lower levels of gut microorganisms.

PCOS stands as the most prevalent hormonal disorder among women of reproductive age and is a leading cause of infertility. Yet, the underlying causes and effective management remain somewhat elusive. For instance, it remains unclear why women with PCOS who do conceive are more susceptible to complications such as miscarriage, premature birth, and gestational diabetes.

Aixia Liu from Z Jiang University in China and her research team tracked the pregnancy outcomes of 220 women across 44 cities, half of whom had PCOS. All were younger than 35 and provided blood samples as well as stool and tissue samples from the endometrial (internal lining of the uterus).

Despite having comparable pregnancy rates, women with PCOS exhibited nearly double the likelihood of facing pregnancy complications, including miscarriage, premature birth, gestational diabetes, and delivering babies with low birth weight. Furthermore, researchers determined that women with PCOS have roughly half the quantity of gut bacteria, particularly Parabacteroides merdae, which was more closely linked to pregnancy outcomes than in those without the condition.

P. merdae aids in converting specific nutrients, like the amino acid isoleucine, into beneficial compounds known as short-chain fatty acids, which are crucial for reproductive health. This likely accounts for the 39% higher average isoleucine levels in the blood samples of PCOS participants and their 10% lower levels of short-chain fatty acids. Additionally, high isoleucine concentrations were noted in the endometrial tissue.

In laboratory settings, when researchers cultured the participants’ endometrial cells and introduced isoleucine, they observed increased markers of cell senescence, indicating wear or damage in the cells that compromised their function. Isoleucine seemed to disrupt the processes endometrial cells typically undergo during pregnancy.

“These findings suggest age-related changes within the uterus,” Li remarked in a statement from the annual meeting of the European Breeding Association, where the data was revealed. “Our research points to high levels of isoleucine from P. merdae potentially impairing endometrial health, even in women under 35.”

Such results suggest that alterations in the gut microbiome could play a role in PCOS-related fertility challenges; however, Andrea Dunaif at the Icahn School of Medicine at Mount Sinai, New York, expresses skepticism. Her studies indicate that reproductive aging in PCOS is more delayed than accelerated. “Reproductive issues often improve in your 30s,” Dunaif notes. “This leads me to doubt the significance of endometrial findings and their true responsibility for pregnancy outcomes.”

Nonetheless, these insights could pave the way for enhanced fertility treatments for women with PCOS. “Where might we intervene in the microbiome and adjust with various probiotics?” Dunaif suggests.