Menstrual synchrony in a sample of working women

Menstrual synchrony has been typically studied among women who live together: dormitory roommates or family members sharing a bedroom or living in the same house. The current study examined menstrual synchrony in 51 pairs of women working together under conditions optimally conducive to synchrony. They had been together for at least 1 year, shared a relatively small office, worked there all day full time and contact with other people during the day was minimal. Prospective records of three menstrual dates showed a significant degree of synchrony for each of the 3 months. Menstrual onsets of close friends tended to occur on the average within 3.5-4.3 days of each other while onsets of co-workers who were not close friends were significantly more broadly ranged (7.7-9.0 days of each other). This is the first unequivocal demonstration of menstrual synchrony outside of the household.