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 with lunar phases. However, neither of them agree on what phase of the lunar cycle menstrual cycles synchronize with. Cutler hypothesizes the synchronization with the full moon and Law with the new moon. Neither offer hypotheses regarding how lunar phases cause menstrual synchrony and neither are consistent with previous studies that found no relationship between menstrual cycles and lunar cycles. More recently, Strassmann investigated menstrual synchrony among Dogon village women. The women were outdoors most nights and did not have electrical lighting. She hypothesized that Dogon women would be ideal for detecting a lunar influence on menstrual cycles, but she