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Medical Description

PCOS, also known as Stein-Leventhal Syndrome, can include the following symptoms or increase a woman’s risk for the following conditions:

  • polycystic ovaries
  • amenorrhea (no menstrual period)
  • infrequent and/or irregular periods
  • infrequent or absent ovulation (oligomenorrhea or anovulation)
  • infertility or subfertility
  • excess hair on the face and body (hirsutism)
  • acne or oily skin
  • thinning of the scalp hair
  • high blood pressure
  • high levels of cholesterol and triglycerides in the blood
  • elevated insulin levels or insulin resistance
  • type 2 diabetes
  • patches of darkened skin (acanthosis nigricans)
  • weight gain or obesity, often with excess weight in the abdomen
  • excess androgen (hormones which produce male sexual characteristics)
  • skin tags

The exact cause of PCOS is unknown. In the past, it was thought that PCOS was caused entirely by the excess production of androgens (also called “male hormones,” although these hormones are usually found in small amounts in women). More recent research has shown that insulin resistance and high levels of insulin (hyperinsulinemia), which appear to cause the overproduction of androgens, play a key role in PCOS (see the link below).

Both insulin resistance and high levels of androgens lead to disturbances in the production of the female hormones, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These are the hormones that control a woman's menstrual cycle and drive ovulation. All of these factors, in turn, contribute to the irregular menstrual cycles and the pattern of missed ovulation of women with PCOS.

The condition is called polycystic ovary syndrome because the ovaries of some women with PCOS appear to have multiple cysts. Hormonal disruptions disturb the normal mechanisms of follicle growth and ovulation. The polycystic appearance of the ovaries is created by follicles, which have failed to develop and release mature eggs (ova). However, not all women with PCOS have ovaries that appear polycystic and not all women with polycystic ovaries have PCOS.

The Role of Insulin in PCOS

Insulin, a hormone made by the pancreas, transports sugar (in the form of glucose) out of the blood and into muscle, fat and liver cells, where it is converted into energy or stored as fat. In women with PCOS, the body cells that are involved in metabolizing sugar are "resistant" to insulin. This means that the process of removing sugar from the blood and allowing it to enter the cells is not working properly and the cells are not responding to insulin as well as they should. The body compensates by producing more insulin.

High levels of insulin can predispose a woman, directly or indirectly, to polycystic ovaries. Not all women with PCOS are insulin-resistant, but most are.

High insulin levels lead to high levels of androgens, through the excessive production of male hormones by the ovary. Increased androgen levels result in menstrual irregularities and other symptoms typical of PCOS. More serious conditions may also develop with PCOS. Women with PCOS are at a greater risk for developing endometrial hyperplasia, in which the uterine lining (or endometrium) thickens to a potentially cancerous stage. (Women with PCOS who ovulate and have regular periods are not at higher risk for endometrial cancer.) Insulin resistance is also associated with a markedly increased risk of type 2 diabetes, as well as an increased risk for gestational diabetes, high blood pressure, high cholesterol and possibly heart disease.


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Polycystic Ovary Syndrome

Medical Description





  • A publication of:
  • Women's College Hospital