Premature Ovarian Failure (POF) is a condition where a woman's ovaries stops working before age 40. Premature Ovarian Failure is different from premature menopause, where a woman's period stops before she is 40. Once that happens, the woman can no longer get pregnant.
Premature Ovarian Failure can have a natural cause or it can be caused by a disease, surgery, chemotherapy, or radiation.Interestingly though, some women still experience occasional periods even with premature ovarian failure.