Menstrual synchrony between mothers and daughters and between roommates.

Menstrual synchrony was examined in three groups of women: 1) mothers and their daughters; 2) women sharing a room in a private residence; and 3) women sharing a room in a dormitory. The intracouple difference in menstrual onset dates was the dependent measure. Mothers and daughters living in the same domicile displayed a significant degree of synchrony. Roommates in private residences were also synchronous, although not significantly more than roommates residing in dormitories.