Higher body-mass index modifies time-resolved maternal autonomic cardiac-uterine coupling during the first stage of human labour.

We investigated whether higher body mass index (BMI) modifies time-resolved maternal autonomic control and maternal cardio-electrohysterographic coupling (MCEC) during the first stage of labour. Seventy-nine women were studied and, for the present analysis, grouped as Control (C; n = 41) and high BMI (HBMI; n = 38). Maternal inter-beat intervals were used to derive time-resolved cardiac sympathetic (CSI) and cardiac vagal (CVI) indices, while uterine activity was obtained from electrohysterography. Compared with controls, HBMI showed higher median CSI and CVI and higher uterine irregularity, consistent with overall autonomic overactivation (increased sympathetic and vagal-related modulation) as captured by these indices. Phase-based coupling analyses indicated a shift in vagal-related phase timing that correlated with BMI as a continuous variable, suggesting that altered MCEC was primarily expressed as a shift in vagal-uterine phase timing. Overall, higher BMI was associated with altered maternal autonomic dynamics and vagal-uterine timing during labour. These findings support BMI-aware, non-invasive intrapartum monitoring as a potential approach to improve physiological interpretation and help guide more individualized labour management.