The symptothermal method is a scientifically recognized procedure for determining the fertile window. It combines daily basal body temperature measurement with observation of cervical mucus . Once you have identified your fertile window, you can use this knowledge to learn more about your cycle.

What does "symptothermal" mean?

The term "symptothermal" already hints at the method used to observe and evaluate a woman's cycle. This term summarizes the two key indicators of fertility. The first indicator ("sympto") is increased vaginal discharge, known as cervical mucus . Additionally, basal body temperature , also called waking temperature ("thermal"), is used to determine the fertile days.

How does the cycle work?

The female menstrual cycle lasts between 21 and 35 days. During this period, fertilization can only occur on six days. After ovulation, the egg can only be fertilized for a maximum of 24 hours , and sperm have a maximum lifespan of five days. This results in a fertile window of six days. The timing of ovulation can vary, and therefore so can the first half of the cycle (the phase from menstruation to ovulation). The post-ovulatory phase is roughly the same length for most women*, between twelve and sixteen days, and hardly changes from cycle to cycle.

This is how the symptothermal method works in everyday life

You can start cycle tracking without a prior doctor's visit, training, or major purchases. All you need is a basal thermometer to measure your waking temperature (basal body temperature) and a way to record it, such as the Ovy app.

The rules used for evaluation can be found in the literature. In the Ovy app, these rules are integrated into the calculation algorithm. It's important that your basal thermometer measures to two decimal places , as the temperature differences that later indicate ovulation are often only in the tenths of a decimal place.

Basically, the following steps should be taken daily: In the morning, immediately after waking up, measure and record your basal body temperature. During the day, note any other symptoms (including cervical mucus) through self-observation. Ideally, begin documenting your data at the start of your cycle, i.e., on the first day of your period. Especially if this method is new to you, try to measure every single day during the first few cycles and diligently record your data.

How safe is the method?

The safety of the method has been confirmed in numerous studies by the so-called Pearl Index (PI). With perfect use, this index is 0.4 (for comparison: pill 0.1, condom 2).

A Pearl Index means that out of 100 women* who used symptothermal contraception for one year (= twelve months or 13 cycles), 0.4 women* became pregnant.

The reliability of the symptothermal method is only achieved in combination with abstinence from sexual intercourse or additional protection on fertile days.

Determining the infertile phase of the cycle

The symptothermal method identifies two infertile phases. The first infertile phase is at the beginning of the cycle, and the second infertile phase is after ovulation. At the beginning of the cycle, the method focuses on prediction, which is less reliable than confirming the infertile phase after ovulation using fertility indicators.

The infertile phase at the beginning of the cycle

At the beginning of the cycle, it's impossible to definitively predict when ovulation will occur, as the symptothermal method is a retrospective method. It makes a prediction based on historical data about when ovulation is unlikely to occur. In this context, the first five days of the cycle can be considered infertile if elevated ovulation was recorded in the previous cycle and no cervical mucus of category "f" or higher was documented at the beginning of the cycle.

The infertile phase at the end of the cycle

During the infertile period after ovulation, it must be clearly established that ovulation occurred before the period is indicated. If the temperature rises and remains elevated, and the cervical mucus changes from fertile to infertile, you can no longer become pregnant.

For beginners, the "strict form" applies.

For women* who are starting this method and want to use a "strict" form of contraception, unprotected intercourse is initially only permitted after ovulation has been confirmed – that is, during the infertile phase after ovulation. They assume they are fertile from the first day of their period. Women* who are new to this method should track their basal body temperature and other symptoms daily for at least three cycles to identify their temperature rise and fall, and thus their ovulation.

If a woman* wishes to have intercourse daily during her fertile window, the symptothermal method only works in combination with a complementary contraceptive method, such as a condom. In this case, the method is as reliable as the chosen complementary contraceptive. Important: The symptothermal method does not protect against sexually transmitted infections.

For whom is the symptothermal method suitable?

After researching the symptothermal method, many women* wonder if this method is suitable for their everyday lives. The method is suitable for the following women*:

• Women* who want to avoid the risks of hormonal contraceptives
• Women* with regular sleep cycles and the willingness to measure and document data daily
• Women* who want to develop an awareness of their cycle and body
• Women* who want to make the best possible predictions about their reproductive health based on digitally recorded data
• Women* who want to have children and find out the day of their ovulation

The symptothermal method is not suitable for the following women* :

• Women* for whom pregnancy is life-threatening
• Teenagers and women* who have severely irregular cycles (for example, longer than 56 days)
• Women* who cannot guarantee a daily measurement at the same time and a sleep window of at least four hours, for example due to travel, shift work, or breastfeeding
• Women* who don't have time for measurement and self-monitoring

Stop taking the pill and get started.

If you're considering switching from a hormonal contraceptive method (pill, vaginal ring, contraceptive patch, IUD) to the symptothermal method, this is perfectly possible. However, a special rule applies to the first cycle, known as the post-pill mode.

You don't need to wait for a full cycle before starting the symptothermal method. Ideally, you should start on the first day of your withdrawal bleeding.

Generally speaking, you should assume you could become pregnant as early as the first cycle after stopping the pill. The first five days are considered infertile, unless fertility is detected earlier based on cervical mucus.

The special feature of post-pill mode is that you need an additional temperature reading; therefore, four consecutive readings, instead of three, must all be higher than the highest of the six preceding readings. However, the third higher reading does not have to be 0.2 degrees Celsius higher.

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