University of Oulu

Maijala, A., Kinnunen, H., Koskimäki, H. et al. Nocturnal finger skin temperature in menstrual cycle tracking: ambulatory pilot study using a wearable Oura ring. BMC Women’s Health 19, 150 (2019).

Nocturnal finger skin temperature in menstrual cycle tracking : ambulatory pilot study using a wearable Oura ring

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Author: Maijala, Anna1; Kinnunen, Hannu2,3; Koskimäki, Heli2,4;
Organizations: 1Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland
2Oura Health, Oulu, Finland
3Optoelectronics and Measurement Techniques Research Group, University of Oulu, Oulu, Finland
4Biomimetics and Intelligent Systems Group, University of Oulu, Oulu, Finland
5Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland
6Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.1 MB)
Persistent link:
Language: English
Published: Springer Nature, 2019
Publish Date: 2020-03-02


Background: Body temperature is a common method in menstrual cycle phase tracking because of its biphasic form. In ambulatory studies, different skin temperatures have proven to follow a similar pattern. The aim of this pilot study was to assess the applicability of nocturnal finger skin temperature based on a wearable Oura ring to monitor menstrual cycle and predict menstruations and ovulations in real life.

Methods: Volunteer women (n = 22) wore the Oura ring, measured ovulation through urine tests, and kept diaries on menstruations at an average of 114.7 days (SD 20.6), of which oral temperature was measured immediately after wake-up at an average of 1.9 cycles (SD 1.2). Skin and oral temperatures were compared by assessing daily values using repeated measures correlation and phase mean values and differences between phases using dependent t-test. Developed algorithms using skin temperature were tested to predict the start of menstruation and ovulation. The performance of algorithms was assessed with sensitivity and positive predictive values (true positive defined with different windows around the reported day).

Results: Nocturnal skin temperatures and oral temperatures differed between follicular and luteal phases with higher temperatures in the luteal phase, with a difference of 0.30 °C (SD 0.12) for skin and 0.23 °C (SD 0.09) for oral temperature (p < 0.001). Correlation between skin and oral temperatures was found using daily temperatures (r = 0.563, p < 0.001) and differences between phases (r = 0.589, p = 0.004). Menstruations were detected with a sensitivity of 71.9—86.5% in window lengths of ±2 to ±4 days. Ovulations were detected with the best-performing algorithm with a sensitivity of 83.3% in fertile window from − 3 to + 2 days around the verified ovulation. Positive predictive values had similar percentages to those of sensitivities. The mean offset for estimations were 0.4 days (SD 1.8) for menstruations and 0.6 days (SD 1.5) for ovulations with the best-performing algorithm.

Conclusions: Nocturnal skin temperature based on wearable ring showed potential for menstrual cycle monitoring in real life conditions.

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Series: BMC womens health
ISSN: 1472-6874
ISSN-E: 1472-6874
ISSN-L: 1472-6874
Volume: 19
Issue: 1
Article number: 150
DOI: 10.1186/s12905-019-0844-9
Type of Publication: A1 Journal article – refereed
Field of Science: 3123 Gynaecology and paediatrics
217 Medical engineering
Funding: Oura Health provided the instruments and devices for the study.
Copyright information: © The Author(s). 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.