What causes polycystic ovary syndrome (PCOS)?
The exact cause of polycystic ovary syndrome (PCOS) is unclear. However, it involves abnormal levels of a number of hormones, including: luteinising hormone, male sex hormones, the female sex hormones progesterone and oestrogen, and insulin. These hormonal changes can prevent the ovaries from releasing fully mature eggs. Usually, once each menstrual cycle during ovulation, one or more eggs are released from the ovaries into the fallopian tubes. The eggs then pass to the uterus, where, if an egg is fertilised, it can develop into an embryo. In PCOS, eggs are not released, but instead form tiny cysts in the ovaries. Over time, these cysts can build up and the ovaries can become 'polycystic'. Because eggs are less likely to be released from the ovaries, women with PCOS are more likely to have problems with fertility.