JMIR Publications

ABSTRACT

Background:

Body temperature is the most used non-invasive biomarker to determine menstrual cycle and ovulation. However, issues related to its low accuracy are still under discussion.

Objective:

This study aimed to improve the accuracy of identifying the presence or absence of ovulation within a menstrual cycle. We investigated whether core body temperature (CBT) estimation can improve the accuracy of temperature biphasic shift discrimination in the menstrual cycle. The study consisted of two parts: Experiment 1 assessed the validity of the CBT estimation method, while Experiment 2 focused on the effectiveness of the method in discriminating biphasic temperature shifts.

Methods:

In Experiment 1, healthy women between the ages of 18 and 40 years had their true CBT measured using an ingestible thermometer and their estimated CBT (calculated from Ts and Ta) measured during sleep in both the follicular and luteal phases of their menstrual cycles. This study analysed the differences between these two measurements, the variations in temperature between the two phases, and the repeated measures correlation between the true and estimated CBT. Experiment 2 followed a similar methodology, but focused on evaluating the diagnostic accuracy of these two temperature measurement approaches (estimated CBT and traditional oral basal body temperature [BBT]) for identifying ovulatory cycles. This was performed using urine luteinising hormone (LH) as the reference standard. Menstrual cycles were categorised based on the results of the LH tests, and a temperature shift was identified using a specific criterion called the "three-over-six rule". This rule and the nested design of the study facilitated the assessment of diagnostic measures, such as sensitivity and specificity.

Results:

The main findings showed that CBT estimated from Ts and Ta during sleep was consistently lower than the directly measured CBT in both the follicular and luteal phases of the menstrual cycle. Despite this, the pattern of temperature variation between these phases was comparable for both the estimated and true CBT measurements, suggesting that the estimated CBT accurately reflected the cyclical variations in the true CBT. Significantly, the CBT estimation method showed higher sensitivity and specificity for detecting ovulation than traditional oral BBT measurements, highlighting its potential as an effective tool for reproductive health monitoring. The current method for estimating the CBT provides a practical and non-invasive method for monitoring CBT, which is essential for identifying biphasic shifts in the BBT throughout the menstrual cycle. This approach is particularly advantageous for analysing menstrual cycles under different environmental conditions by recording temperatures during sleep and accounting for the influence of ambient temperature.

Conclusions:

In conclusion, this study demonstrated that the estimated CBT derived from Ts and Ta during sleep accurately captures variations in true CBT and is more accurate in determining the presence or absence of ovulation than traditional oral BBT measurements. This method holds promise for improving reproductive health monitoring and understanding of menstrual cycle dynamics.