1273 Menstrual Temperature Rhythmicity and its Association with Sleep Duration, Stability, and Efficiency in a Large Wearable Cohort

Abstract Introduction Basal body temperature has long been used for ovulation detection and fertility awareness. With wearable sensors, nightly distal skin temperature can be captured continuously, offering an opportunity to characterize the strength and consistency of these temperature rhythms in daily life. Because physiological systems often interact through shared autonomic, metabolic, and circadian pathways, examining how menstrual temperature oscillations relate to sleep may provide insight into the degree of coupling between reproductive and nightly restorative processes. This study examined whether the strength and stability of menstrual temperature oscillations are associated with sleep duration, sleep efficiency, and night-to-night sleep variability in a large, real-world sample of Oura Ring users. Methods We analyzed longitudinal data from 10,434 Oura Ring users ages 21–55 who logged at least four consecutive menstrual cycles. Nighttime distal skin temperature was modeled using individualized sinusoidal fits based on each user’s cycle length. Per-cycle amplitude and model fit were combined into a cycle coherence index reflecting oscillation strength and model fit quality. We tested associations between cycle coherence and sleep outcomes (duration, efficiency, night to night variability in sleep duration - coefficient of variation), adjusting for age, body mass index (BMI), cycle length, cycle length regularity, and hormone use using Generalized Mixed Effect Models. Results The highest overnight temperature exhibited a pronounced and well-defined oscillatory pattern across the menstrual cycle. Cycle coherence was related to all sleep outcomes, with lower coherence linked to shorter sleep (χ²=154.2; p<.001), lower sleep efficiency (χ²=681.7; p<.001), and greater night-to-night variability (χ²=1001.3; p<.001). Lower coherence was more common in individuals with irregular cycles, atypical cycle lengths, higher BMI, and older age—groups that also showed shorter or less efficient sleep. Conclusion Stronger menstrual temperature rhythmicity was associated with longer, more efficient, and more stable sleep. These findings suggest that temperature-based cycle oscillation patterns, reflected in cycle coherence appear to reflect broader patterns of physiological organization that extend to nightly restorative processes. These findings highlight that wearable-derived temperature signals could help characterize menstrual–sleep interactions and identify individuals with disrupted rhythms. Support (if any) The study was funded by Oura Health Oy (Oulu, Finland).