Contraception

Methods of Contraception: Contraceptive Methods for Women

“Rhythm”
The “rhythm method” of contraception consists simply of abstinence from coitus during a woman's fertile days. Although this method seems easy and effective in principle, it is quite complicated and unreliable in application.
The first problem is to determine the exact number of fertile or "unsafe" days that require coital abstinence. A woman can become pregnant only as long as an egg is in one of her Fallopian tubes. This means that her fertile or "unsafe" days are those shortly before, during, and shortly after ovulation. Abstinence before ovulation is necessary because sperm cells can stay alive inside a woman's body for some time, and abstinence afterwards is necessary because an egg can be fertilized for some time after ovulation. Since menstrual cycles are often irregular and the day of ovulation can therefore not be predicted accurately, one has to allow for a period of at least a week in which an egg could be available for fertilization. To this must be added the possible survival time of sperm cells (up to five days inside the Fallopian tubes), plus another day or two as a margin of safety. Therefore, on the average, the fertile or "unsafe" days add up to about two weeks of each menstrual cycle.
The next question is: When exactly do these two weeks begin? As mentioned above, everything depends on the moment of ovulation. (If it were possible to calculate this moment accurately, the "unsafe" days would be much less than two weeks.) An ovulation usually occurs in the middle of the menstrual cycle or, to be more precise, about two weeks before the beginning of the next cycle. Unfortunately, it is very difficult to predict the beginning of the next cycle. Many women, especially when they are young, or when they are approaching menopause, have irregular cycles, and even for women with regular cycles a variation of two to five days is quite normal.