Originally known as Stein-Leventhal syndrome and discovered in 1935 by Doctors Stein and Leventhal, PCOS (Polycystic Ovary Syndrome) is an endocrine disorder in which women with polycystic ovaries also have one or more additional symptoms. The term polycystic ovaries describes ovaries that contain small cysts almost twice as many as in normal ovaries that are usually no bigger than 8 millimetres each, located just below the surface of the ovaries. These cysts are egg-containing follicles that have not developed properly due to a number of hormonal abnormalities.

Polycystic Ovaries develop when the ovaries are stimulated to produce excessive amounts of male hormones (androgens), particularly testosterone, either through the release of excessive luteinizing hormone (LH) by the pituitary gland or through high levels of insulin in the blood (hyperinsulinaemia).

Polycystic ovaries (PCO) are very common, affecting around 20 per cent of women. Polycystic ovary syndrome (PCOS) is also very common, affecting 5–10 per cent of women. PCOS is one of the leading causes of infertility and if not properly managed, can lead to additional health problems in later life such as diabetes and heart disease.