Cycle day of ovulation

Abstract

The length of the post-ovulatory phase in a composite sample of menstrual cycles increases linearly with cycle length until cycle length reaches about 30 days, but thereafter it ceases to increase (Vollman, 1953; Bailey & Marshall, 1970). By contrast, plotted against the mean cycle length of the individual, the length of the post-ovulatory phase continues to increase roughly linearly with mean cycle length. It is concluded (a) that many long cycles are aberrant occurrences among cycles of normal length and are due to lengthening of the pre-ovulatory phase and (b) that where the mean cycle length is long, ovulation, as in shorter cycles, occurs just before the middle of the cycle, so that the post-ovulatory phase is longer than usual.The most fertile day seems to be the one before mid-cycle. These conclusions are the basis for the following formula for calendar rhythm:If x is the shortest and y the longest cycle in a woman's menstrual record, the ‘unsafe’ days start on Day (½x − 5) and last for (y − x + 8) days.

Can apps and calendar methods predict ovulation with accuracy?

“…As the method of fertile-phase calculation by the examined apps was not available, methods published in the literature that use calendar information alone were examined. These predictive methods were: the standard days method, which predicts days 8-19 of the cycle as fertile days 25 ; the rhythm method, which predicts fertile days using a formula and is based on data from the menstrual records of the past six cycles (the fertile period is predicted as starting on day [x À 18] and ending on day [y -11], where x is the shortest and y is the longest number of days in a woman's menstrual cycle record) 12,26 ; the alternative rhythm method, which predicts fertile days from menstrual records using a different formula (the fertile days start on day ( 1 = 2 x À 5) and last for (y -x þ 8) days, where x is the shortest and y is the longest number of days in a woman's menstrual cycle record 27 ; and the simple calendar method, which subtracts 14 and 15 days from the last cycle length to give the peak fertility days 22 .…”