Association between period of gestation and length of menstrual cycle.

Abstract

It has often been hypothesized that the period of gestation in man may be a multiple of the length of the menstrual cycle. This possibility is suggested because experimental evidence in animals and man has shown cyclic activity in the ovary during pregnancy. A study was done using data on the period of amenorrhea and the length of the cycle for 716 mothers who delivered in 1949 and 1950 in Birmingham England. The shortest mean length of cycle was 23 days for 6 women and 45 days for 1 woman. When the mean length of cycle was recalculated excluding cycles whose lengths were judged to be inconsistent there was a straight line correlation between mean cycle length and period of amenorrhea during pregnancy. The data indicate that the period of amenorrhea increases by about a day for each additional day in the length of the cycle. It is fairly common knowledge that the length of the postovulatory phase is fairly constant in all women being about 14 days. The variation in length of cycle is due to variation in the preovulatory phase. Therefore findings of this study are restated: the variation in the period of amenorrhea according to the length of the menstrual cycle is probably determined by variation in the interval between the onset on menstruation and ovulation.