Temperature method and CO2 method for cycle tracking in comparison

With the Apple Watch Series 8, Apple is making cycle tracking a mainstream topic – and we’re here for it! This is a natural evolution of menstrual tracking, which was first introduced with WatchOS 6. How is it supposed to work though? According to Apple, the wrist temperature sensor on the new Apple Watch Series 8 consists of two temperature sensors – one on the bottom of the watch face and another on the surface of the display that measures “external distortions” when the temperature changes (for example, when your hand is covered by the sheets). Every five seconds, the watch measures the temperature of the wrist and is said to be able to predict retroactively over time when the next ovulation will occur. The results are displayed in the Health app on the iPhone and can also be forwarded from there if needed. The Series 8 was part of a slew of high-profile new products announced at the keynote at Apple Park in California. We think that the topics of menstrual cycles and women’s health might finally get the attention they deserve. But what’s the deal with this method of cycle tracking? How does the temperature method compare to breathe ilo’s CO2 method? And in general, what should one pay special attention to when looking for the most accurate & safe method of cycle tracking?

Methods based on the temperature method can be categorized as a late indicator. The temperature rises from ovulation onwards and thus it is possible to determine ovulation only in retrospect. However, the detection of fertile days before ovulation cannot be done in real time and thus can only be derived by estimating from data based on past cycles. This only works for very, very regular cycles. The breathe ilo method is based on the measurement of the CO2 content in the breath, which drops a few days before ovulation. This makes breathe ilo an early indicator of the start of the fertile window and is based on an actual real-time measurement. 

Let’s compare the temperature method and the CO2 method to see exactly where the differences lie and what the possible advantages/disadvantages might be.

When measuring basal body temperature, the body temperature is measured every morning directly after waking up. In the first half of the cycle, the waking temperature is the normal body temperature of about 36.5 degrees Celsius. After ovulation, it rises by at least two tenths of a degree Celsius. It remains this high until the next period starts. The measurement must be taken directly in the morning, right after waking up and before getting out of bed. You should have slept for a few hours before the measurement. The measurement should be taken for at least three minutes and preferably vaginally or anally. It is also important to mention that within a cycle, measurements should always be taken in the same way and at approximately the same time, and that this method is comparatively more susceptible to external influences. These can include, for example:

 

• illness
• lack of sleep / working shifts
• stress
• time shifts / travel
• alcohol consumption
• change of daily routines

 

If the body temperature rises, this is a sign that ovulation has occurred. If the basal body temperature is at least 0.2 degrees higher on three days in a row than on the previous six days, a woman can assume that ovulation has occurred. In the case of conception, this, unfortunately, means that it is almost impossible to use or determine the fertile days before ovulation in advance. It is only possible to use data from previous cycles to see a pattern.

It has been known in the scientific field since 1951 that there is an alveolar CO2 drop a few days before ovulation. During this period, the alveoli induce a drop in the carbon dioxide content of the body. This effect is due to an excessive increase in breathing rate, called hyperventilation. In other words, you breathe a little faster during your ovulation, which causes more CO2 to be exhaled and the partial pressure of carbon dioxide (pCO2) in your body to drop. This hyperventilation is caused by your hormones and has so far gone unnoticed by women. breathe ilo measures precisely this change in CO2 concentration and thus enables a prediction of the time of ovulation over several days, since the value of pCO2 is higher in the 1st half of the cycle (before ovulation) than in the 2nd half of the cycle (after ovulation). According to science, the CO2 drop happens a few days before ovulation and thus 6 fertile days in the cycle can be assumed. Studies clearly show that most pregnancies occur during this period. This makes breathe ilo the only cycle tracker that can determine ovulation and the individual cycle phases in advance. In addition, our associated cycle app also offers a variety of benefits, such as daily tips and recommendations for the current cycle phase to help users sync their lifestyle to their cycle, as well as a comprehensive knowledge platform where users can proactively acquire more knowledge on the subject of cycle health.