Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder causing infertility in 3 percent to 10 percent of reproductive-aged women. PCOS prevents follicles in the ovary from producing and releasing mature eggs. This results in polycystic ovaries (i.e., ovaries with many small follicles or cysts), infertility and hormonal imbalances.

Fertility specialists define PCOS as the presence of chronic anovulation (not ovulating) or an excess of male hormones (androgens). The precise cause of PCOS is not known.

Missed or Skipped Periods

Chronic anovulation typically leads to "missed" or "skipped" periods. Women with PCOS usually have fewer than eight menstrual cycles per year, and it is not uncommon to skip periods entirely. Anovulation can be caused by chronic hormone abnormalities  including pituitary signaling hormones such as follicle stimulating hormone (FSH) and luteinizing hormone (LH), excess estrogen, decreased progesterone, increased androgens, and insulin resistance.

Excess of Male Hormones

Hyperandrogenism seen in PCOS is an excess of "male" hormones (androgens) such as testosterone and androstenedione. 

PCOS should be diagnosed only after ruling out other potential causes of anovulation and/or hyperandrogenism.