Definition

Usually, frequency in bleeding decreases (oligomenorrhea), followed by complete amenorrhea; however, for many women, bleeding is more frequent, heavier, or prolonged before the onset of oligomenorrhea. Menstrual cycles may vary in length. Menopause is established when menses have not occurred for a year. (Any vaginal bleeding in a woman who has not bled for >= 6 mo must be investigated.) Menopause may be natural, artificial, or premature.

Menopause occurs naturally at an average age of 50 to 51 yr in the USA. As ovaries age, response to pituitary gonadotropins (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) decreases, initially resulting in shorter follicular phases (thus, shorter menstrual cycles), fewer ovulations, decreased progesterone production, and more irregularity in cycles. Eventually, the follicle fails to respond and does not produce estrogen. Without estrogen feedback, circulating levels of LH and FSH rise substantially. Circulating levels of estrogens and progesterone are markedly reduced. The androgen androstenedione is reduced by half, but testosterone decreases only slightly because the stroma of the postmenopausal ovary continues to secrete substantial amounts (as does the adrenal gland). Androgens are converted to estrogens in the periphery, especially in fat cells and skin, accounting for most of the circulating estrogen in postmenopausal women. This transitional phase, during which a woman passes out of the reproductive stage, begins before menopause. It is termed the climacteric or perimenopause, although many persons refer to it as menopause.