JMIR Publications

ABSTRACT

Background:

Oura Ring is a wearable device that estimates ovulation dates using physiology data recorded from the finger. Estimating the ovulation date can aid fertility management for conception or non-hormonal contraception and provides insights into follicular and luteal phase lengths. Across the reproductive lifespan, changes in these phase lengths can serve as a biomarker for reproductive health.

Objective:

This study assessed the performance of Oura Ring’s physiology method of estimating ovulation compared to the traditional calendar method, which estimates ovulation dates based on past menstrual cycle lengths. We evaluate both methods' strengths, weaknesses, and limitations across various factors, including cycle length, cycle variability, and participant age.

Methods:

We applied the physiology and calendar methods to estimate the ovulation dates in 1155 ovulatory menstrual cycles. An ovulation prediction kit (OPK) provided the reference ovulation date, which served as a benchmark to evaluate the accuracy of each method. Performance metrics included the error in days between the estimated and reference ovulation dates and the percent of ovulations detected.

Results:

The physiology method outperformed the calendar method, with a mean absolute error (MAE) of 1.26 days compared to 3.44 days. Both methods demonstrated stable performance across adults aged 18 - 52. Cycle variability did not impact the physiology method’s performance; however, the calendar method had performance significantly worse in participants with irregular cycles, with an MAE of 6.63 days. The cycle length presented challenges for the physiology method, with a slightly reduced detection rate in cycles shorter than 26 days (from 98% in typical cycles to 93% in short cycles). Specifically, physiology method error was stable in cycle lengths up to 35 days but increased from an MAE of 1.18 to 1.70 days in abnormally long cycles. However, the physiology method still far outperformed the calendar method in abnormally long cycles, which had an MAE of 7.32 days.

Conclusions:

The Oura Ring’s physiology method estimates ovulation dates with approximately 2.7 times greater accuracy than the calendar method in typical menstrual cycles. For users with abnormally long or irregular cycles, the calendar method’s accuracy significantly diminishes, whereas the physiology method remains relatively stable, experiencing only minor reductions for detection in shorter cycles and slight accuracy declines in abnormally long cycles. These findings highlight the limitations of the calendar method, especially in atypical cycles, and underscore the enhanced reliability of the physiology method.