The calendar-tracking method, or rhythm method, is one way people monitor and record their periods, but it might not be the most accurate. That’s according to a new study released Monday by the Journal of Medical Internet Research.
Also: Your next smart ring or Apple Watch could have a feature that transforms healthcare
The study, written by Oura’s Head of Science, VP of Health Sensing, and lead machine learning data scientist, found that Oura’s physiology method, which powers its Fertile Window feature, outperformed the calendar method. The Oura Ring 3, Oura’s earlier smart ring that released in 2021, was used in the data collection for this study.
Oura’s physiology method vs the calendar method
The Fertile Window feature estimates when during a person’s cycle they are most likely to conceive and is an ovulation prediction tool for those trying to avoid or get pregnant. Oura also has a partnership with hormone-free birth control brand Natural Cycles, which tracks a user’s fertility status by monitoring their body temperature.
The study was performed on 964 participants from Oura’s commercial database and included 1,155 menstrual cycles. Out of those menstrual cycles, the physiology method used by Oura detected 1,113 ovulations, resulting in an accuracy rate of 96.4%. The calendar method produces an average error of 3.44 days, whereas the physiology method in the study produced an error of 1.26 days.
Also: Why Oura Ring 4 is ZDNET’s product of the year – besting Samsung, Apple, and others
Think of the physiology method as the secret sauce behind the Oura Ring’s Fertile Window feature. It’s an algorithm written in Python and developed using a training set of 30,000 menstrual cycles. It analyzes temperature data to estimate when a user has begun ovulation.
The physiology method is eating the calendar method’s lunch. Eighty-two percent of cycle estimations were within two days of the reference ovulation date using the Oura Ring and the physiology method, compared to 32.5% of cycle estimations using the calendar method.
“The physiology method had significantly better accuracy across all cycle lengths, cycle variability groups, and age groups compared with the calendar method,” the authors wrote in the study. Wrist wearables, like a Garmin or Apple Watch, reported ovulation detection rates between 54% and 86%, far lower than Oura’s 96.4% detection rate, the study found.
Smart rings are getting smarter and more accurate
For longer or irregular cycles, the physiology method produced less accurate results. It detected fewer ovulations in shorter-than-average cycles, but the researchers wrote, “did not differ between typical and long or abnormally long cycles.”
The researchers wrote that calendar-based fertility tracking, while not as accurate, could still be used as a backup if a user confronts “insufficient physiology data,” but they stress that the calendar method must be used with caution, especially among those with irregular menstrual cycles.
Also: Oura Ring’s new Symptom Radar feature could predict your next cold. How it works
“Our analyses suggest the physiology method can reliably estimate ovulation dates for adults aged 18-52 years, across a variety of cycle lengths, and in users with regular or irregular cycles. This method may be used as a tool to improve fertile window estimation, which can aid in conceiving or preventing pregnancies. This method also offers a low-effort solution for follicular and luteal phase length tracking, which are key biomarkers for reproductive health,” the authors wrote.
The findings of the study prove that smart ring data collection is getting even smarter and more accurate — and cements Oura as a reliable ovulation tracker and predictor.
