JMIR Publications

ABSTRACT

Background:

As a daily point measurement, basal body temperature (BBT) might not be able to capture the temperature shift in a menstrual cycle because a single measurement is located on the sliding scale of the circadian rhythm. Wrist skin temperature measured continuously during sleep has the potential to overcome this limitation.

Objective:

To compare the diagnostic accuracy of the two temperature measurements for detecting ovulation and to investigate the correlation and agreement between the two measurements in describing thermal changes of menstrual cycles.

Methods:

This prospective study included 193 cycles (170 ovulatory and 23 anovulatory) collected from a convenience sample of 57 healthy women. Participants wore a wearable device (Ava Fertility Tracker bracelet 2.0) that continuously measured wrist skin temperature during sleep. Daily BBT was measured orally and immediately upon awakening using a computerized fertility tracker with a digital thermometer (Lady-Comp). An at-home luteinizing hormone (LH) test was used as the reference standard of ovulation. The diagnostic accuracy of using at least one temperature shift detected by the two temperature measurements in detecting ovulation was evaluated. For ovulatory cycles, repeated measures correlation was used to examine the correlation between the two measurements, and mixed effect models were used to determine the agreement between the two temperature curves at different menstrual phases.

Results:

Wrist skin temperature was more sensitive than BBT (sensitivity: 0.624 vs. 0.229, P<.0001) and had a higher true positive rate (54.9% vs. 20.2%) to detect ovulation; however, it also had a higher false positive rate (8.8% vs. 3.6%), resulting in lower specificity (0.261 vs. 0.696, P=.002). The probability that ovulation had occurred when at least one temperature shift was detected was 86.2% for wrist skin temperature and 84.8% for BBT. Both measurements had low negative predictive value (8.8% for wrist skin temperature, and 10.9% for BBT). Significant positive correlation between the two measurements was only found in the follicular phase (rrm=0.294; P=.001). Both measurements showed an increase of temperature during the postovulatory phase with greater increase for wrist skin temperature (range of increase: 0.50°C vs. 0.20°C). During the menstrual phase, wrist skin temperature exhibited a greater and more rapid decrease (from 36.13°C to 35.80°C) than BBT (from 36.31°C to 36.27°C). During the pre-ovulatory phase, changes of both temperature measurements were minimal and there were small variations in estimated daily difference between the two measurements, indicating agreement between the two curves.

Conclusions:

For women interested in maximizing the chances of pregnancy, wrist skin temperature continuously measured during sleep is more sensitive than BBT to detect ovulation. The difference in diagnostic accuracy of these methods was likely due to the greater temperature increase in the postovulatory phase and greater decrease during the menstrual phase for the wrist skin measurements. Clinical Trial: The study was registered in the ClinicalTrials.gov database (identifier NCT03161873).