Menstruation menarche has changed little in the United States since the 1950s. Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days). Perimenopause is when fertility in a female declines, and menstruation occurs less regularly in
Menstrual cycle half months postpartum. There is a wide range of response among individual breastfeeding women, however, with some experiencing return of menstruation at two months and others remaining amenorrheic for up to 42 months postpartum. The word "menstruation" is etymologically related to "moon". The terms "menstruation" and "menses" are derived from the Latin "mensis" (month), which in turn relates to the Greek "mene" (moon) and to the roots of the English words "month" and "moon". Even though the average length of the human menstrual cycle is similar to that of the lunar cycle, in modern humans there is no relation between