The Methods of Controlling Birth by Natural Means

Rhythm Method

In the natural rhythm of the monthly menstrual cycle, there is a spell of approximately eight to ten days during which the egg produced by the ovaries can be fertilized. If the sexual intercourse takes place only during the remaining 18 or so days, and is avoided during the 'unsafe' time the woman cannot in theory become pregnant. That is the basis of the rhythm, or natural method of birth control.

Unfortunately, because the menstrual cycle varies in both length and regularity in many women, the rhythm method is not as safe a form of contraception as, for example, the birth control pill, condom or intrauterine devices.

The risks can, however, be reduced by using a combination of three methods to estimate when, during the month, it should be safe to have sexual intercourse: the calendar method; the temperature method; and the ovulation or Billings method.

The Calendar Method

This should never be relied upon by women whose menstrual cycles are short or irregular. Using this method, the first day of menstruation is counted as Day 1. A woman with an absolutely regular 28 day cycle will have her 'unsafe' time - when intercourse should be avoided - between Day 9 and Day 18.

For greater security, note the precise length of each menstrual cycle over 12 months. The first unsafe day can then be worked by deducting 19 from the shortest of the last 12 cycles. If the shortest cycle was 25 days, conception is possible from Day 6 (25-19). The last unsafe day is calculated by deducting 11 from the longest of the cycles. If the longest was 31 days, the last unsafe day is Day 20 (31-11).

In this example, conception is therefore possible from Day 6 until Day 20 inclusive. Intercourse would be safe from Day 1 to Day 5 inclusive (there is no medical reason for avoiding intercourse during menstruation, although many have aesthetic or religious objections) and from Day 21 to the end of the cycle.

Temperature Method