What causes polycystic ovarian syndrome?

Polycystic ovarian syndrome (PCOS) is one of the most common—and least understood—hormonal problems in women, and it’s a major cause of infertility. But a new study offers insights into what’s causing PCOS.

We've long known that women with PCOS have too many male hormones, like testosterone and androstenedione, in their bodies. That causes symptoms like acne, excessive facial hair, and thinning hair, as well as irregular ovulation, which can make it difficult to get pregnant.

But until now, it hasn’t been clear exactly why women produce these extra male hormones. Since women with PCOS are more likely to be overweight and to develop diabetes, the leading theory is that it’s somehow related to insulin resistance. But that doesn’t answer one of the mysteries around PCOS: while it’s known to run in families, researchers haven’t been able to find a gene linked to it.

Now, a new study published in the journal Nature Medicine has found that a hormone called anti-Müllerian hormone (AMH) may be to blame.

AMH is produced when the ovaries release an egg, so it’s normally low during pregnancy, but when the researchers looked at AMH levels in 66 pregnant women with PCOS, they found that they had levels almost a third higher than pregnant women without the syndrome.

Then, to determine whether elevated AMH was causing the PCOS or just a side effect of it, they injected AMH into pregnant mice. Those mice gave birth to daughters that were more likely to have PCOS-like issues, including having fewer babies when they grew up. Somehow, a high AMH level in mothers seemed to lead to PCOS in the next generation.

High AMH levels during pregnancy is a novel explanation for how PCOS might develop, says Jeffrey Roberts, an OB/GYN, reproductive endocrinologist, infertility specialist and co-director of the Pacific Centre for Reproductive Medicine in Burnaby, BC. “These are very interesting findings,” he says, adding that it supports a theory that women with PCOS may have such high AMH levels that eggs can’t mature fully.

Can cetrorelix treat PCOS?

The researchers also tested using a drug called cetrorelix in the mice with PCOS. The drug blocks gonadotrophin hormones, which limits ovulation, and thus lowers AMH levels as well. They found that the mice on cetrorelix stopped having PCOS symptoms.

But cetrorelix might not be the solution women suffering from PCOS are looking for. For one thing, it's not an answer for PCOS sufferers who are trying to conceive because it essentially shuts down a woman's cycle, says Roberts. There are other treatments—including drugs like letrozole or follicle-stimulating hormone—which work fairly well, with 60 percent of women becoming pregnant when they use them.

While cetrorelix may relieve other PCOS symptoms, Roberts isn’t convinced that it’s a good option. He cautions that it might be too strong of a drug to be a reasonable solution. Cetrorelix requires a daily injection and currently costs nearly $100 a day.

“It makes sense that if you shut the menstrual centres down with cetrorelix, symptoms of PCOS are reduced, but there are other ways to suppress the menstrual cycle that we have used for many years for treatment of PCOS,” says Roberts. The most common one? The birth control pill. Weight loss is another commonly recommended treatment.

If you’re suffering from PCOS, talk to your doctor about the best treatment options for you.

Read more:
What happens after you go off the birth control pill
6 ways to increase your chances of getting pregnant