Can We Trust Wearable Sensors for NFP? A Look at the New Tempdrop Study and NC° Band
I love to learn about technology benefitting women’s health. In the NFP space, much of the Femtech I am familiar with relates to thermometers and charting apps. Three recent headlines caught my attention:
New Study: How Accurate is Tempdrop?
In the SymptoPro program that I teach, our methods are based on research with basal body thermometers. A concern with using a wearable device instead of a basal thermometer is that we don’t know the technology and algorithms used to determine the temperature, as the wearable device tracks axillary temperature throughout the night.
A recent study, Accuracy of an Overnight Axillary-Temperature Sensor for Ovulation Detection: Validation in 194 Cycles, authored by Yaniv Shpaichler, Alicia Thompson, Benedicte Fromager, Michael Vardi, and Rene Ecochard, shed some light on this topic.
125 women participated in this study, and 194 cycles were analyzed. The women wore the Tempdrop armband to track temperature throughout their cycles, and they used the Clearblue Connected Ovulation Test System to track the LH surge, which is a precursor to ovulation. The study found that, when compared to the Clearblue tests, Tempdrop’s algorithm correctly identified the day of ovulation within a 5-day window in 93.3% of cycles and showed a 98.6% accuracy in determining fertile vs. non-fertile days.
These results definitely give me more confidence in relying on Tempdrop’s data to track my cycles. There are two key factors I want to keep in mind:
When charting for family planning, knowing the actual day of ovulation isn’t vital (or, frankly, possible without an ultrasound). We know that sperm can survive up to 5 days if egg-white cervical mucus is present, so we always want to be aware of the fertile window.
We don’t need Femtech to pinpoint ovulation for us; if we know our bodies (and take a program like SymptoPro), we can determine our fertile and infertile windows.
It was also interested to read about the temperature sensor itself. The study states:
First, it measures the temperature of the skin above the axillary artery. This location is one of the places where skin temperature most closely resembles internal body temperature, as it is near a large blood vessel and if the measurement is taken for more than 12 min, it closely corresponds with the core body temperature. In addition, the device has a second temperature sensor that measures the ambient temperature. This enables the device to identify periods when the arm is closed and in contact with the chest, i.e., when the temperature measurement is most accurate.
In short, Tempdrop measures skin temperature near a major artery, and filters out “cold” air when the arm is open/away from the body.
I’ve always wondered how Femtech companies decide where the device should be worn on the body (arm, wrist, finger, etc.). Since skin temperature is distinct from basal body temperature, it’s reassuring to know that the temperature on the upper arm where Tempdrop is placed is close to internal body temperature.
Natural Cycles: Is It Worth Trying Their New Wristband?
Natural Cycles is a popular cycle tracking app. It recently launched its own wearable device to measure temperature, called the NC° Band. According to Natural Cycles, the NC° Band is worn on the wrist and tracks temperature, movement, and heart rate during sleep. The heart rate and motion data help determine if the wearer is asleep and if there are any changes in her routine. The wristband can then sync with the Natural Cycles app, and the app will indicate whether or not she is fertile or infertile that day. It’s important to note that the Natural Cycles app has been able to connect to other wearable devices like Oura Ring and Apple Watch to track temperature.
While I have been using Tempdrop for a couple years, I have never tried the NC° Band. It’s great that the NC° Band makes charting temperature more accessible, as the band itself is just under $100 (though there is a subscription fee to use the app). I like how more women, in theory, are aware of the biomarkers that change throughout their cycles, depending on their hormones. However, I have a few concerns:
What is the accuracy of wearing the device on your wrist? Do temperatures become less accurate when the device is worn toward extremities? While this is just a personal observation, I’ve noticed in my clients that those who wear Oura ring or an Apple Watch have had more erratic temperature patterns.
The Natural Cycles app offers predictions of fertility. I may be biased, but I firmly believe that we should not rely on an app to tell us when we are fertile or not. We should make that decision ourselves once we have had appropriate training from a certified instructor. With a program like SymptoPro, we also crosscheck cervical mucus and temperature biomarkers so that we are not relying on one observation.
Wearable devices can make temperature-taking for cycle tracking way more convenient. With a traditional basal body thermometer, it’s important to wake up around the same time every day to take the temperature, also making sure that you’ve had sufficient sleep before waking. A wearable device mitigates that concern. However, when making decisions on wearable devices, it is important to keep up-to-date on research studies and news, since you will be relying on their data to help you determine your fertility status. That is also why it is important to observe other biomarkers like cervical mucus.
You can receive 10% off of Tempdrop with my referral code HERE. I do not officially endorse these products and cannot guarantee their quality or performance. I may receive a small commission when you make a purchase using my Tempdrop code. For informational purposes only.
About the author: Rachel Fields is a certified SymptoPro instructor, teaching women how to practice natural family planning using the sympto-thermal method.