Predicting ovulation is important because a woman only ovulates once per month.
The ovulated egg can only survive for 24 hours. In most women, ovulation occurs about 14 days prior to the onset of bleeding, which in the ideal menstrual cycle of 28 days, would be day 14. However, since the length of the cycle varies depending of the length of the first half, ovulation does not always occur on the same day.
Basal Body Temperature for Predicting Ovulation
An inexpensive method of determining the day of ovulation is to chart the basal body temperature (BBT) each morning prior to arising from bed. In the first half of the cycle the normal basal temperature is around 97° F. Twelve (12) to 24 hours after ovulation the temperature rises to the standard 98.6° F. The BBT is good for documenting ovulation, but is less desirable for timing intercourse, as the temperature rise begins only after ovulation has occurred. It really is not necessary to chart more than one or two cycles with the BBT, as by that time, the answer should be apparent if ovulation is taking place.
Ovulation Prediction Kits
Ovulation predictor kits, which can be purchased at most pharmacies and supermarkets, are more useful for timing intercourse, as they can predict when ovulation is going to occur, before it happens. They function by measuring the spontaneous LH surge in the urine (like a home pregnancy test), which is the trigger for, and precedes normal ovulation. A positive test indicates that ovulation will be occurring in the next 12-36 hours and can be used to time intercourse and inseminations, as well as provide information regarding the length of the second half of the cycle.