Polycystic ovarian syndrome, or PCOS, is a condition in which a woman’s levels of the sex hormones estrogen and progesterone are out of balance. This leads to the growth of ovarian cysts (benign masses on the ovaries). PCOS can cause problems with a women’s menstrual cycle, fertility, cardiac function, and appearance. Symptoms often begin soon after a woman first begins having periods. In some cases, PCOS develops later during the reproductive years, for instance, in response to substantial weight gain. Symptoms include irregular menstruation such as menstrual intervals longer than 35 days; fewer than eight menstrual cycles a year; failure to menstruate for four months or longer; and prolonged periods that may be scant or heavy.