Monitoring Basal Body Temperature Rhythm: Abdominal Skin Temperature Measurements Taken During Sleep as Simpler Alternative

This study developed a clip-on wearable temperature logger to continuously measure abdominal skin temperature (AST) during sleep for menstrual rhythm monitoring. The suitability of AST measurement as an alternative to traditional sublingual basal body temperature (sBBT) measurements was also examined. The goal was to track the biphasic BBT pattern and identify the transition from low to high temperatures, a critical indicator of ovulation. We analyzed 100 menstrual cycles from 41 women with regular cycles. The device was clipped onto underwear directly on the abdominal skin near the navel and automatically recorded AST every 10 min during sleep. Concurrently, sublingual temperatures were taken every morning to create a traditional BBT chart. Ovulation was confirmed using a urine test for luteinizing hormone (LH) surge, which served as a reference point for validating the accuracy of both methods. The highest AST reading each night (AST maxima) was used for comparison with the sBBT data. The average AST maxima closely matched the average sBBT, exhibiting a high correlation across the menstrual cycle. Then, the dates of the temperature transition from low- to high-temperature phases, based on sBBT and AST maxima, were compared with the LH-positive date for validation. The transition dates detected by both methods were similar, with no significant difference in their averages. The results revealed that AST maxima and sBBT exhibit a similar temperature pattern, indicating that the AST-based temperature chart could be a simpler alternative to the traditional BBT chart.