kalenterimenetelmä

The kalenterimenetelmä, often translated as the "calendar method" or "rhythm method," is a natural family planning technique used to avoid or achieve pregnancy. It relies on tracking a woman's menstrual cycle to estimate her fertile and infertile periods. The fundamental principle is to abstain from or use barrier methods of contraception during the days of the cycle when ovulation is most likely to occur, thus reducing the chance of fertilization.

To implement the kalenterimenetelmä, a woman must accurately record the length of her menstrual cycles for at least six consecutive months. The shortest cycle is used to calculate the first fertile day, and the longest cycle is used to calculate the last fertile day. For example, if a woman's shortest cycle was 26 days, she would subtract 18 to estimate the first fertile day (day 8 of her cycle). If her longest cycle was 30 days, she would subtract 11 to estimate the last fertile day (day 19 of her cycle). The period between these calculated days is considered the fertile window.

The effectiveness of the kalenterimenetelmä is highly variable and dependent on the regularity of a woman's menstrual cycle and strict adherence to the method. Irregular cycles significantly reduce its reliability. Studies show a wide range of effectiveness, with typical use failure rates being considerably higher than those for other contraceptive methods. Therefore, it is often recommended for couples who are highly motivated, have very regular cycles, and are willing to accept a higher risk of unintended pregnancy. Its use may also be combined with other fertility awareness methods, such as basal body temperature charting or cervical mucus monitoring, to improve accuracy.