A woman's body provides three basic ways to identify the fertile and infertile times of her cycle. Recognizing the patterns of those physical signs forms the basis for all methods of natural family planning. A woman learns to identify the normal, healthy cervical mucus which indicates when a pregnancy is most likely to occur. Due to normal hormonal activity, a woman's resting temperature changes during the menstrual cycle. Lower temperatures indicate that ovulation has not yet occurred.
Higher temperatures indicate a rise in progesterone which signals the end of the fertile time.
The third stage is a change in the shape or texture of the cervix. Finally, secondary signs such as minor abdominal pain or pressure at the time of ovulation can also be observed. Natural family planning is not calendar rhythm. It did not account for individual differences. Modern advances in the science of NFP make it possible to profile each woman's individual cycle.