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 synchrony Israel. Twenty seven families, which had from two to seven sisters 13 years or older and collected data on menstrual cycle onsets over a three-month period. Using the methods of, they reported menstrual synchrony occurred for the first two months, but not for the third month for roommate sisters, close friend roommates, and for families as a whole. Strassmann investigated whether menstrual synchrony occurred in a natural fertility population of Dogon village women. Her study consisted of 122 Dogon women with an average lifetime fertility rate of 8.6 ± .3 live births per woman. Their median cycle length was 30