Abstract
Core and peripheral body temperatures are affected by changes in reproductive hormones during the menstrual cycle. Women worldwide use the basal body temperature (BBT) method to aid and prevent conception. However, prior research suggests that taking one’s daily temperature can prove inconvenient and subject to environmental factors. We investigate whether a more automatic, non-invasive temperature measurement system can detect changes in temperature across the menstrual cycle. We examined how wrist skin temperature (WST), measured with wearable sensors, correlates with urinary tests of ovulation and may serve as a new method of fertility tracking. One hundred and thirty-six eumenorrheic, non-pregnant women participated in an observational study. Participants wore WST biosensors during sleep and reported their daily activities. An at-home luteinizing hormone (LH) test was used to confirm ovulation. WST was recorded across 437 cycles (mean cycles/participant = 3.21, S.D. = 2.25). We tested the relationship between the fertile window and WST temperature shifts, using the BBT three-over-six rule. A sustained 3-day temperature shift was observed in 357/437 cycles (82%), with the lowest cycle temperature occurring in the fertile window 41% of the time. Most temporal shifts (307/357, 86%) occurred on ovulation day (OV) or later. The average early-luteal phase temperature was 0.33°C higher than in the fertile window. Menstrual cycle changes in WST were impervious to lifestyle factors, like having sex, alcohol, or eating prior to bed, that, in prior work, have been shown to obfuscate BBT readings. Although currently costlier than BBT, the present study suggests that WST could be a promising, convenient parameter for future multiparameter fertility awareness methods.
Highlights
The biphasic basal body temperature (BBT) rhythm during the menstrual cycle has been reported and studied since the early 1900s [1], with the first observational study taking place in the 1960s [2]
We demonstrated that the rhythm of skin temperature during menstrual cycle as measured by a wrist-worn wearable shows a biphasic pattern in 82% of the cycles, which is comparable with the results obtained in prior studies using BBT
Skin temperature could be a potentially useful parameter to be combined with other physiological measurements correlating with the onset of the fertile window and with ovulation for a more comprehensive modern fertility awareness method
Summary
The biphasic basal body temperature (BBT) rhythm during the menstrual cycle has been reported and studied since the early 1900s [1], with the first observational study taking place in the 1960s [2]. A woman’s BBT reaches its lowest point (nadir) in a given cycle around her fertile window, just prior to ovulation and corresponding to a peak in estrogen [4]. Prior work suggests that sperms can survive in the female genital tract for up to 6 days, with higher probability of conception occurring closer to ovulation [5,6,7]. A dip in BBT may indicate imminent ovulation; after ovulation occurs, a woman’s BBT typically increases as c 2018 The Author(s).
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