Like HowStuffWorks on Facebook!

The Basics of Menopause

        Health | Menopause

The change of life. The end of fertility. The beginning of freedom. Whatever people call it, menopause is a unique and personal experience for every woman. It's a natural event that marks the end of fertility and childbearing years. Technically, menopause results when the ovaries run out of eggs and decrease production of the sex hormones estrogen, progesterone and, to a lesser extent, androgen.

Why or how does this happen? A woman is born with about 500,000 egg cells, but only about 400 to 500 ever mature fully to be released during the menstrual cycle. The rest degenerate over the years. During the reproductive years, a gland in the brain generates hormones that cause a new egg to be released from its follicle each month. As the follicle develops, it produces the sex hormones estrogen and progesterone, which thicken the lining of the uterus. This enriched lining is prepared to receive and nourish a fertilized egg, which could develop into a fetus. If fertilization does not occur, estrogen and progesterone levels drop, the lining of the uterus breaks down, and menstruation occurs.

For reasons unknown, your ovaries gradually begin to change in hormone production during your mid-30s. In your late 40s, the process accelerates and hormones fluctuate more, causing irregular menstrual cycles and unpredictable episodes of menstrual bleeding. By your early to mid-50s, periods finally end altogether. However, estrogen production does not completely stop. The ovaries decrease their output significantly, but still may produce a small amount of estrogen.

The other female hormone

Progesterone, the other female hormone, works during the second half of the menstrual cycle to prepare the uterine lining as a viable home for an egg, and to shed the lining if the egg is not fertilized. If you skip a period, your body may not be making enough progesterone to break down the uterine lining. However, your estrogen levels may remain high even though you are not menstruating. At menopause, hormone levels don't always decline uniformly. Production of estrogen and progesterone is erratic and unpredictable at this time.

Most women can tell if they are approaching menopause because their menstrual periods start changing. The "menopause transition" is a term used to describe this time. Perimenopause is another term used by some to describe as "being in menopause." But menopause itself — as defined by health care professionals — is only one day in a woman's life — the day after she has not had a menstrual period for 12 consecutive months, and no other biological or physiological cause can be identified. Until 12 consecutive months have passed without a menstrual period, a woman in her late 40s may still be able to get pregnant, despite irregular periods.

Although the majority of women experience "natural" or spontaneous menopause, some women may experience menopause due to one of a number of medical interventions. Surgically removing both ovaries, a procedure known as bilateral oophorectomy, will trigger menopause, at any age. Induced menopause can also occur if the ovaries are damaged by radiation, chemotherapy or by certain drugs. Certain medical conditions also may cause menopause to occur earlier.

Copyright 2003 National Women's Health Resource Center Inc. (NWHRC)