NATURAL FAMILY PLANNING—

PERIODIC ABSTINENCE

This method is based on avoiding sexual intercourse around the time of
predicted ovulation. It assumes the egg is fertilizable for 12–24 hours and sperm
is capable of fertilizing the egg for 24–48 hours. It requires a high degree of
discipline from both sexual partners. Methods include prediction or
identification of ovulation inferred from menstrual records, basal body
temperature charting (temperature rise from thermogenic effect of progesterone),
and change in cervical mucus from thin and watery to thick and sticky (reflects
the change from estrogen dominance preovulation to progesterone dominance
postovulation).

Advantages: inexpensive,    readily available,  no  steroid hormonal    side-effects,

may be  preferred   for religious   reasons

Disadvantages:  inaccurate  prediction  of  ovulation,  high    failure rate    because

of  human   frailties   and the passions    of  the moment