Should you trust calendar contraception?

By | October 16, 2021

How does it work?

Although the menstrual cycle usually lasts about a month, pregnancy can only occur within a couple of days after ovulation. If you add a few days during which the sperm remain active, you get six to seven fertile (i.e. fertile) days. The difficulty is that you can only see ovulation with an ultrasound examination, and it is impossible to predict its date with absolute accuracy. True, you can focus on the length of the monthly cycle and use formulas to roughly determine the fertile period.

The classic calendar method is the calculation of “dangerous” and “safe” days based on the length of the cycle. With a serious approach, you need to start with keeping the menstrual calendar for at least eight months, and preferably a year. After that, the first fertile day is calculated from the duration of the shortest cycle, and the last day is calculated from the duration of the longest. During fertile days, the chances of pregnancy are high, which means that you should either avoid sex or use condoms.


It is clear that the accuracy of calculations and the effectiveness of such contraception leaves much to be desired, especially with an unstable menstrual cycle. To determine the period of fertility more reliably, you can measure basal temperature, that is, body temperature early in the morning, immediately after waking up. The fact is that it decreases slightly the day before ovulation, and then rises by 0.3-0.6 degrees.

Special thermometers for determining basal temperature differ from ordinary ones in that they measure with an accuracy of two decimal places. After waking up, you need to measure the temperature under the tongue, and then enter the result into a special schedule.

Even during the monthly cycle, the consistency of the mucus covering the cervix changes; these changes are also sometimes taken into account in conjunction with counting days and measuring temperature to better distinguish fertile days from “safe” days. True, not everyone is ready to closely examine the consistency of mucus, and the changes are not always obvious to a layman. Nevertheless, the method is often recommended , only not for contraceptive purposes, but vice versa – for those who are trying to get pregnant.

Advantages and disadvantages

The main advantage of calendar or temperature contraception is the absence of side effects. Although hormonal contraceptives are improved every year, sometimes their selection takes an agonizingly long time, and the ideal one may never be found (especially when you consider that about ten times fewer such drugs are registered in Russia than in the United States). It has recently been confirmed that hormonal contraception, including pills and intrauterine devices, increases the likelihood of increased depression by 40%. On the other hand, hormonal drugs are indicated for many women to correct excess androgens (male sex hormones), to treat acne or painful and difficult menstruation.

The calendar method of contraception is also called “natural family planning” and “the method of intermittent abstinence”, and these terms describe its features well, which are not suitable for every couple. If you do not want to get pregnant, you will have to use condoms or refuse sex on your fertile days . If pregnancy is not specifically planned, but also does not frighten (“if I get pregnant, I will give birth”), then it would be good to normalize the lifestyle, cure chronic diseases, if any, and increase physical activity. In any case, the calendar method requires concentration and good sleep patterns; it is hardly suitable for those who fly on business trips every week (try to get enough sleep and remember to carry a thermometer with you).

Measuring temperature, counting days, and keeping a calendar requires more discipline than, for example, taking a daily pill. Spontaneous sex is poorly combined with the calendar method, even in a long-formed couple, let alone new partners (however, in such cases, you always need to use condoms to protect yourself not only from pregnancy, but also from infections). And yet, the main problem of the calendar method is low reliability: its Pearl index is from 9 to 40, that is, pregnancy can occur in 40 women out of 100 (almost half!) Within a year. But it looks like this situation is starting to change thanks to smartphone apps.

Can reliability be improved?

There are many menstrual tracker and ovulation calculator apps out there , but they are usually designed to determine the best days to conceive, not the other way around. The apps aimed at preventing pregnancy were mostly limited to pill reminders and trackers telling you when it was time to change your hormonal vaginal ring. But in February 2017, Natural Cycles became the world’s first smartphone app to register as a contraceptive medical device; the basis was the results of two full-fledged clinical studies.

The “contraceptive” application for a smartphone uses the calendar-temperature method (also called symptothermal). Users do not have to draw graphs – they just need to measure the temperature under their tongue with a sensitive thermometer every morning and enter it into the application, and it will do the rest by itself using mathematical algorithms.

According to the creators of the application, the percentage of fertile days mistakenly called safe does not exceed 0.5%, that is, with ideal use, the method is very reliable. It turns out that, thanks to a complex algorithm, the effectiveness of the calendar method of contraception approached that for hormonal drugs. On the other hand, in a study of the real use of this application among more than 4,000 women, the Pearl index, which determines the effectiveness of contraceptive methods, was 7%.

This means that pregnancy occurred in 7 women out of 100 per year, but most often it was not an application error that was to blame, but a human factor, for example, unprotected sex during the fertile period or inaccurate temperature measurement. At its accuracy is affected by factors such as colds, hangovers or lack of sleep. Sleeping too long (two hours longer than usual) also reduces the accuracy of the thermometer, so it’s not clear what to do with the habit of getting enough sleep on weekends. Of course, like any other method of contraception, this one is not for everyone; on the one hand, it is devoid of side effects and is now surprisingly accurate, and on the other, it requires a stable lifestyle, discipline and certain restrictions.

Considering that the trend towards the use of “natural” and “organic” has not slowed down for a year, and the registration of Natural Cycles in Europe as a medical device has become a sensation (the application is used by more than one hundred and fifty thousand people), it is possible that other similar ones will appear . Relative cheapness (65 euros per year, including a thermometer) can be a plus for many, eliminating any inconvenience. In the end, the more options there are, the more likely each woman will choose the option that suits her best.

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