ABSTRACT
Periodic Abstinence (Rhythm Method) If coitus takes place outside the fertile period, i.e. 6 days before and 2 days after ovulation, then the chance of pregnancy is low (see Chapter 16, Figure 1). The day of ovulation can be determined by daily basal body tem perature measurements and assessment of the cervical mucus. At ovulation the temperature rises 0.2-0.6°C and cervical mucus ceases to be stringy. Because the ovulated ovum survives at the most for 2 days, the woman is reli ably infertile thereafter. Unfortunately, ovulation fre quently occurs earlier in the cycle than the median day 14. Hence, the preovulatory infertile phase is less reliable than the postovulatory. The rhythm method has the sanction of religious groups opposed to other forms of contraception, and is widely practiced with success. It is not suitable for women with irregular periods in whom the time of ovulation cannot be predicted with any certainty.
