Psychosocial and biological influences on menstruation: synchrony, cycle length, and regularity.

The purpose of the study was to determine some psychosocial and biological variables as predictors of menstrual synchrony, menstrual cycle length, and menstrual regularity. One-hundred-and-seventy subjects at two all-women colleges kept monthly menstrual records and answered questions about their backgrounds, menstrual histories, and social habits. They also took the Personality Research Form E. Subsets of the total subject group were used in different analyses. Both psychosocial and biological factors were found to predict individual differences in menstrual synchrony among 80 of the women studied. In a group of 144 women, cycle length and cycle regularity were found to depend, in part, on age at menarche. Psychosocial and personality traits also predicted cycle length and regularity. As a group, 86 women did not significantly synchronize their cycles with those of their roommates, although there was a trend towards synchrony. Certain characteristics particular to this sample may have accounted for this finding, including cycles that were relatively long and irregular compared with those reported in other studies. The results support the concept that menstrual cycle variables depend on personality and psychosocial factors as well as on biological ones.