How does the rhythm method work?
The post-ovulatory infertility phase is calculated by deducting 10 from your longest menstrual cycle. For example, if your longest cycle was 32 days, then 10 from 32 would be 22.
Therefore, on the 22nd day of your cycle you would resume another infertile period. This would also mean that, from day 8 to 21 of any given cycle, it would be necessary for you to abstain from sex or use another contraceptive method, as the likelihood of pregnancy is significantly increased at this time.
Who Can Use It?
Most natural birth control methods need you to be very aware of each and every change that occurs in your body. Knowing the length of your monthly cycles, noticing the changes in your cervical mucus and paying attention to changes in your body temperature can all help to keep you aware of your fertility.
Therefore, those who have irregular cycles cannot really benefit from the Calendar Rhythm Method. Additionally, teenagers, who often do not have regular cycles yet, are also advised against using this method.
Because this method requires the use of periodic abstinence, it is recommended more often for people in long-term relationships.
Furthermore, the rhythm method offers no protection against STDs, like HIV and chlamydia. This is another reason why it is more often recommended for couples in long-term, monogamous relationships where both partners have tested free of STDs.
It is always better to consult your physician before practising this method, as he will be able to advise on the exact way you can track your cycle and if you need to use any other devices that might help in knowing your ovulatory phase.
Imperfect use of this birth control option or having intercourse during the fertile days has lead to a relative increase in the failure rate of rhythm method.
Of about 100 women using this method, around 25 may get an accidental pregnancy. Even with perfect use, though, the rhythm method is still only 91% effective meaning, out of 100 women who use this method perfectly, nine will be become pregnant every year.