Daily Step-Count and Sleep Metrics Across Pregnancy: An Observational Analysis of the LEAP Cluster Randomized Controlled Trial

Abstract Study Objectives We investigated daily associations between step count and sleep quality across trimesters using wearable devices. Methods Participants (N=243; pre-pregnancy BMI ≥ 25 kg/m2 ) from a mobile health RCT intervention arm, wore Fitbits day and night from ~8 weeks’ gestation- delivery. Devices tracked daily step count (primary exposure), moderate to vigorous physical activity (MVPA) and light physical activity (LPA) (secondary exposures), and sleep measures (duration, stage length, efficiency, awakenings, midpoint and multidimensional sleep score). Covariate-adjusted mixed effects models estimated daily associations between movement and sleep outcomes, stratified by trimester. Results Participants averaged 5,795 steps/day. In trimester 1, step count (per 1,000) was associated with shorter sleep duration (-23 minutes, OR=0.84, 95% Confidence Interval (CI): -38.7, -8.6, In the trimester 2, step count was associated with shorter sleep duration (-22 minutes, CI: -27.6, -16.4), shorter light sleep (-10 minutes, CI: -13.3, -6.6), longer deep (+4 minutes, CI: 2.7, 6.1) and REM sleep (+6 minutes CI: 3.5, 7.7). In trimester 3, step count was associated with lower odds of poor sleep (OR=0.84, CI: 0.70, 1.00), shorter light sleep (-14 minutes, CI: -18.4, -9.3), longer deep (+6 minutes, CI: 3.3, 7.8) and REM sleep (+8 minutes, CI: 5.5,11.4), and more awakenings (+0.9, CI: 0.4, 1.4). Associations of MVPA and LPA with sleep were smaller in magnitude but relatively consistent with step count. Conclusions Higher daily step count was associated with higher quality sleep in the following night during second and third trimesters. These findings highlight step count as a potential target to support prenatal sleep quality. Statement of Significance High quality sleep is a vital aspect of whole-body and mind health for pregnant individuals. In our study, we used device-based longitudinal data to illustrate the relationship of wearable device-recorded daily step-count and physical activity minutes on sleep quality in pregnant individuals across trimesters. We showed that engaging in more steps led to improvements in overall sleep quality and sleep architecture, with the strongest effects observed in the third trimester. We also found shorter sleep duration on days with higher step count or MVPA, potentially due to reductions in light sleep. This paper highlights the importance of daily steps and activity, regardless of intensity, and acknowledges the complexity of sleep hygiene by adjusting for key confounders. Future directions include exploring potential mediators of the PA-sleep relationship in pregnancy.