PIP: Natural methods of family planning make use of the naturally occurring signs and symptoms of the fertile and infertile phases of the menstrual cycle. Recognizable signs and symptoms occur cyclically, and women can be taught to recognize them. Changes take place in basal body temperature, cervical mucus, and the cervix uteri. Basal body temperature rises about .2 degrees C (.4 degrees F) immediately after ovulation when the blood levels of progesterone increase. Following menstruation, cervical mucus is composed of cense cellular matter that forms an impenetrable barrier (typeG). As the cycle progresses under the influence of increasing estrogen, there is a predominance of characteristically lumpy opaque mucus (type L). A few days before ovulation, the characteristically thin slippery crystal clear stretchy mucus is produced (type S). Fertile mucus is composed of a combination of L-type and S-type mucus. Estrogen casuses changes to take place in the muscle and connective tissue of the cervix. As estrogen levels rise during the pre-ovulatory phase, the cervix softens and the cervical os opens. A woman can be aware of these changes by gently palpating the cervix with her finger tip. These signs and symptoms which reflect accurately the rise and fall of the hormones estrogen and progesterone are the basis of fertility awareness on which natural methods of family planning are based. In addition to knowing when ovulation takes place, it is also necessary to know the length of time the ovum can be fertilized after ovulation and the life span of the sperm in the female genital tract before ovulation. In fertile mucus, sperm will live an average of 3 days, but it must be understood that it is possible for sperm to survive for 5 days if conditions are right. To make allowances for sperm survuval, the fertile phase starts when follicular development begins and estrogen levels start to rise. The life span of the ovum is less than 24 hours. Natural family planning methods--including the temperature method, the ovulation method (Billings), the calandar method (rhythm), and the sympto-thermal method are explained.