| The principle of this method is to refrain from
sexual intercourse during the ovulation period 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 for a long period in order to predict the fertile period.
Therefore it is not very reliable for women with irregular cycles, or whose cycles are
affected by illness, childbirth or 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 co-operative. The main advantage of this method is that it is free
from side-effects, and may be the only method of birth control acceptable to some couples
with religious backgrounds.
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