Periodic abstinence is also called natural family planning, safety period or rhythm method. The principle of this method is to avoid sexual intercourse around ovulation when the woman is most fertile. Ovulation usually occurs 14 days before the onset of the next menstruation. The fertile period can be estimated by the calendar method, charting daily basal body temperature, or detecting changes in cervical mucus. However since menstrual cycles are not always regular, the user needs careful and persistent charting over a long time in order to predict the fertile period. Therefore it is not reliable for women with irregular cycles, or whose cycles are affected by illness, childbirth or peri-menopause. The various methods used for estimating the fertile period also require careful instruction and some couples may find it difficult to abstain from sexual intercourse during the fertile period unless they are strongly motivated and cooperative. The main advantage of this method is that it is free from side-effects.
