Menstrual and reproductive characteristics and age at natural menopause.

Data from women who enrolled between 1935 and 1939 in a long-term prospective study of menstrual and reproductive health, in which menstrual cycles and other events were recorded as they occurred, were analyzed to examine factors associated with age at natural menopause. Analysis was restricted to 561 women who enrolled before age 25 years and recorded data through at least age 44 years. Women with a median cycle length that was less than 26 days at ages 20-35 years reached menopause 1.4 years earlier than those with cycles between 26 and 32 days. The difference in mean menopausal age between women with short cycle length (less than 26 days) and women with long cycle length (33 days or longer) was 2.2 years. Women who had ever been pregnant reached menopause slightly, but statistically significantly, later than women who had never been pregnant. Similarly, women who had ever had a live birth had a slightly later age at menopause compared with nulliparous women. A trend of later age at menopause with increasing parity was also observed. There was no association with age at menarche. Certain of these observations are consistent with proposed mechanisms of cessation of menstrual function.