Timing is everything.
Many years ago scientists discovered that among the side effects of ovulation are a slightly higher body temperature and a drying up of cervical mucus. It is a technique of fertility control based upon making love during only the naturally infertile or relatively infertile time of a woman's menstrual cycle. A menstrual cycle has three phases. Phase one extends from the first day of menstruation to the beginning of the most fertile phase. It is relatively infertile.