How Natural Family Planning Works
Natural family planning is also known as "the rhythm method." Natural family planning uses a variety of methods that seek to prevent pregnancy by either avoiding intercourse around the time of ovulation or using knowledge of the time of ovulation to use other methods such as condoms, diaphragms or spermicides.
Natural family planning is a safe, inexpensive method of contraception and may be more acceptable than other forms of contraception for moral, ethical or religious reasons. Natural family planning is a good method of contraception for couples who are highly motivated, and who have a regular menstrual cycle. The major drawback with its use is the loss of sexual spontaneity or the need to abstain from intercourse during the "fertile" portion of the menstrual cycle.
The "fertile" period is based on calendar calculations, variations in basal body temperature, changes in cervical mucus or more commonly a combination of these methods. For a woman with an absolutely regular 28-day cycle, the fertile period lasts from days 10-17. Additional days are added to the fertile period based on the time of the shortest and longest menstrual interval. For example, if your periods are every 31 days (28 days + 3 days), the fertile period would be from day 13 (10 +3) to day 20 (17+3). On the other hand, if your period is every 25 days, the fertile period would be from day 7 (10-3) to day 14 (17-3).
Basal body temperature is measured by taking your temperature when you wake up each morning before you do any activity, or take anything by mouth. A rise in your basal body temperature of 0.5 to 1oF indicates ovulation. When the cervical mucus becomes thin, "stretchy," and clear, ovulation is about to occur. Therefore, using this method, couples should avoid intercourse from four to five days after menses begins until two to three days after the temperature rise or from the first awareness of the clear, copious mucus until four to five days afterwards. The "safe" interval is determined when the mucus becomes milky and thick in appearance.
Other more sophisticated methods can be used such as ovulation detection kits. However, for the most part, these methods are expensive to use on a monthly basis.