Menstrual disorders and month of birth.

Menstrual characteristics in a population of 23,227 women who participated in a breast cancer screening programme were considered with respect to month of birth. High and low risk months of birth were defined according to the seasonal preovulatory overripeness ovopathy (SPrOO) hypothesis. Positive associations were found in 11 out of the 14 relations studied. The results were significant for early menarche (< or = 11 years), long menstrual cycles (> or = 5 weeks), menorrhagia (> or = 7 days and profuse blood loss), and early (< or = 40 years) or late (> or = 56 years) menopause. The results not only confirm the birth excess of these women in specific months, as has been found by others. They apparently agree with the SPrOO hypothesis and with a transgenerational concept of familial subfecundability along matrilineal lines and hence, familial clustering of pathological progeny, independent of Mendelian rules.