Basal body temperature is measured at rest for 5 minutes after waking up with a thermometer inserted under the tongue. Many women perceive this as a morning routine burden; this may lead to missing data, because they forget to take measurements, or data errors from falling asleep during the measurments. To overcome this, a wararable device called Ran's night were developed to automatically measures abdominal skin temperature during sleep. In this study, we examined the diagnostic accuracy of abdominal skin temperature in detecting ovulation compared to basal body temperature. Abdominal skin temperatures were automatically measured for six hours during sleep by placing a wearable in-clothes thermometer between underwear. BBT were also measured upon waking each morning. If the body temperature on three consecutive days is higher than the last six days before, it is assumed that ovulation has occurred. The ovulation reference date was detected by LH urinalysis. For 202 cycles obtained from 45 healthy women, the sensitivity in detecting one temperature shift per cycle were 85.9% and 80.1% for basal body temperature and abdominal skin temperatures, respectively. The deviation from the ovulation reference date was 0.2±2.5 days for sublingual temperature and 0.4±2.7 days for abdominal skin temperature, with no significant difference. In addition, a strong correlation (0.703) was obtained for the difference between the two corresponding to the same period. These results indicate that abdominal skin temperature can be used to estimate the date of ovulation with the same accuracy as basal body temeperature.
