The very word "menopause" is being redefined. Although it is commonly used to refer to the transition between women's reproductive and postreproductive years, the World Health Organization (WHO) has adopted the literal meaning "a stop in menses, or menstruation." This definition limits menopause to a single point -- a year from the date on which the last period began. On average, women have their last menstrual periods at age 50 or 51 (smokers a year or two earlier), but menstruation can end much earlier or much later. Approximately 8% of women stop having periods before age 40. Such premature menopause sometimes runs in families. It can also result from chemotherapy or radiation treatments. Surgical menopause, the removal of both ovaries in a procedure known as ovariectomy or oophorectomy, can occur at any age.

The word "perimenopause" (literally, around menopause) is defined by the WHO as beginning when a woman's menstrual cycles start to vary from her usual pattern and ending a year after menopause -- that is -- 2 years after her last period. This formal definition is open to interpretation. Some endocrinologists place the beginning of perimenopause even earlier -- when ovulation and fertility begin to decline sharply, usually in a woman's late 30s. Perimenopause is, in essence, another word for "going through menopause." It is the time when women are most likely to have symptoms, such as hot flashes and night sweats.

Postmenopause begins a year after menopause and lasts for the rest of a woman's life. For postmenopausal women, the risks of certain conditions, including osteoporosis, heart disease, Alzheimer's disease, breast cancer, and colorectal cancer, increase steadily -- the result of aging as well as declining estrogen levels.

From the Harvard Health Publications Special Health Report, Managing Menopause. Copyright 1999 by President and Fellows of Harvard College. All rights reserved.