Polycystic (literally, many cysts) ovary syndrome (PCOS or PCO) is a complex condition that affects the ovaries (the organs in a woman's body that produce eggs). In PCOS, the ovaries are bigger than average, and the outer surface of the ovary has an abnormally large number of small follicles (the sac of fluid that grows around the egg under the influence of stimulating hormones from the brain).

In PCOS, these follicles remain immature, never growing to full development or ovulating to produce an egg capable of being fertilised. For the woman this means that she rarely ovulates (releases an egg) and so is less fertile. In addition, she does not have regular periods and may go for many weeks without a period. Other features of the condition are excess weight and excess body hair.

The condition is relatively common among infertile women and particularly common among women with ovulation problems (an incidence of about 75 per cent). In the general population, around 25 per cent of women will have polycystic ovaries seen on ultrasound examination but most have no other symptoms or signs of PCOS and are perfectly healthy. The ultrasound appearance is also found in up to 14 per cent of women on the contraceptive pill.

The ways in which PCOS shows itself include:

• absent or infrequent periods: a common symptom of PCOS. Periods can be as frequent as every five to six weeks, but might only occur once or twice a year, if at all.
• increased facial and body hair (hirsutism): usually found under the chin, on the upper lip, forearms, lower legs and on the abdomen (usually a vertical line of hair up to the umbilicus).
• acne: usually found only on the face.
• infertility: infrequent or absent periods are linked with very occasional ovulation, which significantly reduces the likelihood of conceiving.
• overweight/obesity: a common finding in women with PCOS because their body cells are resistant to the sugar-control hormone insulin. This insulin resistance prevents cells using sugar in the blood normally and the sugar is stored as fat instead.
• miscarriage (sometimes recurrent): one of the hormonal abnormalities in PCOS, a raised level of luteinising hormone (LH - a hormone produced by the brain that affects ovary function), seems to be linked with miscarriage. Women with raised LH have a higher miscarriage rate (65 per cent of pregnancies end in miscarriage) compared with those who have normal LH values (around 12 per cent miscarriage rate).

These symptoms are related to several internal changes.

Hormonal abnormalities, including:

• raised luteinising hormone (LH) in the early part of the menstrual cycle.
• raised androgens (male hormones usually found in women in tiny amounts).
• lower amounts of the blood protein that carries all sex hormones (sex-hormone-binding globulin).
• a small increase in the amount of insulin and cellular resistance to its actions.

Characteristic changes in the appearance of the ovaries on ultrasound scan. The ovaries are polycystic, with many small follicles scattered under the surface of the ovary (usually more than 10 or 15 in each ovary) and almost none in the middle of the ovary. These follicles are all small and immature, generally do not exceed 10mm in size and rarely, if ever, grow to maturity and ovulate.

Most women with PCOS will have the ultrasound findings, whereas the menstrual-cycle abnormalities are found in around 66 per cent of women and obesity is found in 40 per cent. The increase in hair and acne are found in up to 70 per cent whereas the hormone abnormalities are found in up to 50 per cent of women.

It is likely that there are different stages of the disease throughout life. Younger women tend to have substantial difficulties with their periods, whereas older women have other problems such as diabetes and high blood pressure, though their period patterns tend to become more regular. Women with PCOS also have an increased risk of strokes and heart attacks, but their death rate from these conditions is not increased (Wild et al, 2000). Women with PCOS may also have an increased risk of endometrial cancer (cancer of the lining of the womb), particularly if they have infrequent or absent periods.