Natural family planning is really a form of periodic abstinence from sex, or not having sex at those times of the month when a woman is fertile. The trick is knowing just what are the safe and not so safe times. Obviously, it is essential for both sexual partners in this situation to cooperate fully in the contraceptive process. The man must be as aware of the woman's cycle as she is herself. For this reason alone, this method of contraception does not suit all couples. There are many different ways of calculating the fertile time of the month. The most common is a simple mathematical calculation, as a woman usually ovulates 14 days before her next period starts. If the woman has a regular cycle, there is no problem, but if her cycle varies significantly, other clues to ovulation must be observed. Changes in body temperature can give a guide to ovulation, as the temperature first dips, then rises about half a degree centigrade at the time of ovulation. Changes in vaginal secretions also occur just before ovulation, and these can be noted on a glass slide. Breast tenderness and lower abdominal pain may be other relevant signs in some women.
The Billing's method of contraception is a combination of the above factors. Because sperm can live for a number of days in the woman after ejaculation, and because the woman is fertile for two or three days after ovulation every month, sex must be avoided for six to eight days during every cycle. The failure rate of this method can vary widely, and depends a great deal on the couple's commitment to follow the rules strictly, and the woman's own ability to note her own bodily changes. The percentage of women falling pregnant in one year while using natural family planning as varied from 5% to 25% in different clinical studies. Natural family planning can be used in combination with other forms of contraception, such as condoms, spermicidal foam or diaphragms, which are used at the time of the month when pregnancy may occur. No couple should undertake this form of contraception without consulting a doctor who understands, and is prepared to teach, natural family planning.