Comparison of a wearable core temperature sensor with rectal thermometry during high-intensity interval running in pregnant and non-pregnant women.
- 1Department of Sports Medicine, Norwegian School of Sports Sciences, Norway.
- 2Medical Service Institute, Norwegian Armed Forces, Norway.
Abstract
Background
An increasing number of pregnant women, including elite athletes, continue vigorous- and high-intensity exercise during pregnancy. Current pregnancy exercise guidelines primarily recommend at least 150 min of moderate-intensity physical activity per week and provide limited specific guidance on vigorous- and high-intensity exercise in highly trained pregnant women. High-intensity exercise can elevate core temperature (Tcore), raising concerns about maternal hyperthermia and potential fetal risks (e.g. neural tube defects, preterm birth, fetal growth restriction). Accurate monitoring of maternal Tcore may be necessary to evaluate safety. However, pregnancy-related cardiovascular and thermoregulatory adaptations, such as changes in skin blood flow and heat dissipation, may affect temperature estimates, yet few non-invasive and user-friendly methods combine accuracy with practicality during exercise. This study compared the non-invasive CALERA Research Sensor (CRS) with a rectal probe, the gold standard for Tcore measurement, during high-intensity interval running in pregnant and non-pregnant participants.Methods
Thirty elite and recreational athletes participated, including 15 pregnant participants (31 ± 4 years) and 15 non-pregnant participants (30 ± 6 years). All completed a separate 10-min warm-up, followed by up to five 5-min high-intensity treadmill-intervals separated by recovery periods. Testing was conducted under environmental conditions of 20-21°C and 38-61% relative humidity. Analyses included the intervals, corresponding pauses, and 20 min of post-exercise, during which no cool-down was performed. Agreement was assessed using Bland-Altman plots, with a pre-defined ±0.3°C acceptability threshold. Differences were analyzed using paired t-test.Results
Nearly half of the measurements exceeded the predefined threshold (47% in pregnant vs. 43% in non-pregnant participants), reflecting systematic bias between methods. In pregnant participants, the mean difference (rectal probe - CRS) was -0.23°C (95% CI: -0.36, -0.09°C), indicating that CRS overestimated Tcore relative to the rectal probe. In contrast, in non-pregnant participants, the mean difference was 0.16°C (95% CI: 0.03, 0.28°C), indicating that CRS underestimated Tcore. Discrepancies were most pronounced during the early intervals but diminished over time.Conclusion
This study shows opposing systematic bias of CRS in pregnant and non-pregnant women compared with Tcore measured using a rectal probe, limiting its use as a stand-alone tool in pregnancy and highlighting the need for non-invasive temperature sensor development.
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BibTeX
@article{brevikpersson2026comparison,
title = {{Comparison of a wearable core temperature sensor with rectal thermometry during high-intensity interval running in pregnant and non-pregnant women.}},
author = {Sofia Brevik-Persson and Jørgen Melau and Emilie Mass Dalhaug and Christina Gjestvang and Lene A H Haakstad},
journal = {Journal of exercise science and fitness},
year = {2026},
month = oct,
doi = {10.1016/j.jesf.2026.200529},
url = {https://europepmc.org/article/MED/42921436},
note = {CC BY},
}
RIS
TY - JOUR
TI - Comparison of a wearable core temperature sensor with rectal thermometry during high-intensity interval running in pregnant and non-pregnant women.
AU - Sofia Brevik-Persson
AU - Jørgen Melau
AU - Emilie Mass Dalhaug
AU - Christina Gjestvang
AU - Lene A H Haakstad
PY - 2026
DA - 2026/10/01
JO - Journal of exercise science and fitness
DO - 10.1016/j.jesf.2026.200529
UR - https://europepmc.org/article/MED/42921436
AB - Background An increasing number of pregnant women, including elite athletes, continue vigorous- and high-intensity exercise during pregnancy. Current pregnancy exercise guidelines primarily recommend at least 150 min of moderate-intensity physical activity per week and provide limited specific guidance on vigorous- and high-intensity exercise in highly trained pregnant women. High-intensity exercise can elevate core temperature (Tcore), raising concerns about maternal hyperthermia and potential fetal risks (e.g. neural tube defects, preterm birth, fetal growth restriction). Accurate monitoring of maternal Tcore may be necessary to evaluate safety. However, pregnancy-related cardiovascular and thermoregulatory adaptations, such as changes in skin blood flow and heat dissipation, may affect temperature estimates, yet few non-invasive and user-friendly methods combine accuracy with practicality during exercise. This study compared the non-invasive CALERA Research Sensor (CRS) with a rectal probe, the gold standard for Tcore measurement, during high-intensity interval running in pregnant and non-pregnant participants.Methods Thirty elite and recreational athletes participated, including 15 pregnant participants (31 ± 4 years) and 15 non-pregnant participants (30 ± 6 years). All completed a separate 10-min warm-up, followed by up to five 5-min high-intensity treadmill-intervals separated by recovery periods. Testing was conducted under environmental conditions of 20-21°C and 38-61% relative humidity. Analyses included the intervals, corresponding pauses, and 20 min of post-exercise, during which no cool-down was performed. Agreement was assessed using Bland-Altman plots, with a pre-defined ±0.3°C acceptability threshold. Differences were analyzed using paired t-test.Results Nearly half of the measurements exceeded the predefined threshold (47% in pregnant vs. 43% in non-pregnant participants), reflecting systematic bias between methods. In pregnant participants, the mean difference (rectal probe - CRS) was -0.23°C (95% CI: -0.36, -0.09°C), indicating that CRS overestimated Tcore relative to the rectal probe. In contrast, in non-pregnant participants, the mean difference was 0.16°C (95% CI: 0.03, 0.28°C), indicating that CRS underestimated Tcore. Discrepancies were most pronounced during the early intervals but diminished over time.Conclusion This study shows opposing systematic bias of CRS in pregnant and non-pregnant women compared with Tcore measured using a rectal probe, limiting its use as a stand-alone tool in pregnancy and highlighting the need for non-invasive temperature sensor development.
SN - 1728-869X
SN - 2226-5104
ER -