Menopause is the permanent cessation of menstruation resulting from loss of ovarian follicular activity.

Menopause is preceded by a perimenopausal period, starting when the first features of impending menopause begin (ie, irregular menstrual bleeding and cycle frequency) and lasting until at least 1 year after the final menstrual period.

During the menopausal transition, gonadotropins, estradiol, and inhibin show a marked degree of variability in their circulating levels. Within 1–2 years after the final menstrual period or the onset of menopause, FSH levels are markedly elevated, LH levels are moderately high, and estradiol and inhibin levels are low or undetectable. The resultant ovarian changes include short follicular phases with early ovulation and luteal insufficiency characterized by lower levels of progesterone secreted for shorter periods of time compared with the luteal phase of younger women. Postmenopausally, adrenal androstenedione is the major source of estrogen, and serum testosterone levels decrease moderately.

Starting from age 36 years, ovarian follicular apoptosis accelerates, leading to a steady decline in ovarian estradiol production (Figure 9–13). This loss of ovarian function results in a 90% loss of circulating estradiol; serum estradiol concentrations are often lower than 20 pg/mL. However, extragonadal estrogen synthesis increases as a function of age and body weight, and most of the estradiol is formed by extragonadal conversion of testosterone. The predominant estrogen in menopausal women is the weak estrogen estrone, produced through aromatase conversion of androstenedione.