The use of wearable devices for predicting biphasic basal body temperature to estimate the date of ovulation in women

The basal body temperature (BBT) in women is biphasic, with high- and low-temperature phases during the menstrual cycle. Biphasic BBT predicts the date of ovulation for contraception and family planning. Although the BBT is measured with a basal thermometer at rest, upon waking up, it is often tedious to measure for women. Additionally, the single measured values are not sufficient to reflect biphasic BBT. To solve these problems, various wearable devices have been developed. In the present review, we introduce these devices, compare them to other available basal thermometers, and discuss possible future devices. Wearable devices used to measure skin temperature, ear canal temperature, and temperature in clothes during nighttime to predict BBT (the type of bracelet, ring, armband, ear, and waist), have been developed. These devices are convenient for users, because they measure and record temperature automatically during the nighttime instead of every morning. The scientific evidence was most documented for the type of bracelet, wherein the wrist skin temperature measured during the nighttime reflected the biphasic BBT and predicted the date of ovulation. The popular wearable device, FitbitⓇ measures the wrist skin temperature; in addition, the recent patent information states that the Apple WatchⓇ might have added the same function. Although there have been no previous studies, these devices might reflect biphasic BBT, because they are similar to bracelets. These devices are popular in the healthcare market; therefore, their function to measure wrist skin temperature may supplant other devices to predict the date of ovulation in the future.