Fertility Awareness Methods

Calendar-Rhythm Method

Average Failure Rate: 13-20%

The calendar method, or rhythm method, is the oldest and most widely practiced method of fertility awareness. Early in the twentieth century, the rhythm method was promoted by the Catholic Church as the only morally acceptable form of family planning. At one time the Calendar-Rhythm Method was synonymous with natural family planning. However, since that time many other natural methods have been developed and the modern Catholic Church accepts all of these.

How the Calendar-Rhythm Method Works

In the 1920s, it was discovered that ovulation occurs about fourteen days before the next menstrual period. Based on this discovery, it was possible to calculate the best times to have intercourse to achieve or avoid pregnancy. The Calendar-Rhythm Method based on three assumptions:

1. That ovulation occurs fourteen days before the beginning of menstruation, plus or minus two days


2. That sperm remain alive for three days, and


3. That the ovum (egg) survives for twenty-four hours.

For a woman with very regular cycles, she needs merely to count backwards from the first day of her period to locate the day on which she ovulated, usually the fourteenth day from the first day of her period. Using this information, she can predict when ovulation will occur the following month and avoid having intercourse around that time.

Efficacy of the Calendar-Rhythm Method

Most women do not ovulate at the same time every month, and no woman's cycles are identical each time. For this reason, the rhythm method is not very effective unless your cycle is always the same number of days. For women with very regular cycles, the failure rate is probably closer to 13%. This method is completely ineffective if used improperly.

Considerations for Using the Calendar-Rhythm Method

This method is rarely taught any longer, and thus is not described here in detail. If you are interested in using this type of method, consider the standard days method instead, which is easier and more effective. The calendar-rhythm method offers no protection from sexually transmitted disease.

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