Can knowledge of the fertile phase be used for effective contraception?

Rhythm Method

As sperm can survive for seven days, there are probably no 'safe' days between cessation of the period and ovulation (Q13.4). Fertility awareness (e.g. rhythm methods) has one of the highest failure rates of contraceptive methods (Pearl Index)but there are no side effects and the method is acceptable to some cultures more than others. If ovulation can be predicted accurately, intercourse from two days onwards would theoretically be unlikely to result in conception. Ovulation occurs 14 days before the next period. Calculation of the post ovulation 'safe' period is easier for those women with a regular cycle. Ultrasound has shown that ovulation pain (Mittelschmerz) tends to begin 24 48 hours before ovulation.

The basal temperature can be used as a guide to the timing of ovulation. Following ovulation, progesterone is produced (Fig 2. 3)

And this results in the temperature rising by 0.5 degree centigrade. The temperature should be basal rather than after activity and is generally measured in the morning on waking. If you record your temperature for a couple of months and feel confident that your chart shows clear changes this method may have advantages if you are reluctant to use other methods. From the medical point of view this method is not regarded as being effective.

Assessment of the cervical mucus provides an indication of ovulation but it is not reliable. Progesterone, which is released into the circulation after egg release and though the second half of your menstrual cycle, makes the mucus less profuse and more sticky.

The rhythm or calendar method involves calculation of the shortest and longest cycles over the last twelve cycles. The fertile phase is calculated as 20 days subtracted from the shortest cycle and 11 days from the longest cycle. If the cycle is regularly 28 days the fertile phase would be from Day 8 (28-20) until Day 17 (28-11). If the cycle varies from 21 to 35 days, the fertile phase would be from Day 1 to Day 24. For those with irregular cycles there may be few safe days.

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