Menopause is the time when a woman's menstrual periods stop and her ovaries stop releasing eggs. A woman is considered menopausal once she has gone a year without having a menstrual period. Therefore, the exact time of a woman's final menstrual period can only be pinpointed by counting backwards after the fact.
Although most women go through menopause around age 50, normal menopause can happen any time between the age of 40 and 60. The last periods are usually more irregular and have less blood flow. But some women's periods don't change at all.
Along with normal or natural menopause, there is also premature menopause. Premature menopause occurs before the age of 40 and can be caused by a variety of things, such as removal of the ovaries, autoimmune disorders, endocrinological reasons, or cancer therapy. Medical interventions, such as a hysterectomy (removal of the uterus), may also prevent menstruation. If the ovaries are removed as well, production of the hormones estrogen and progesterone are stopped, causing the symptoms of menopause.
Menopause is a normal part of the aging process. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by the pituitary gland as part of the normal menstrual cycle. They stimulate the ovary to produce estrogen and progesterone and to release an egg. As a woman ages, her ovaries don't respond to FSH or LH as strongly as they used to. Over time, less and less estrogen and progesterone are produced and the woman stops releasing eggs.
Premature menopause can be genetic or it can be caused by autoimmune diseases. These diseases produce antibodies that can damage the ovaries. Surgical removal of the ovaries causes artificial menopause, as can chemotherapy or radiation therapy to the pelvis to treat cancer.