Effects of low maternal heart rate on fetal growth and birthweight

Objective To evaluate the association between birthweight and maternal heart rate (MHR) or heart rate variability (HRV) under resting conditions at 20–24 gestational weeks and 34 weeks or later (34+ weeks). Methods Data were retrospectively reviewed from the Safe Passage Study, a prospective longitudinal cohort study of alcohol use in pregnancy and birth outcomes in Cape Town, South Africa, between August 2007 and January 2015. Using custom‐designed software, MHR and indicators of HRV were obtained from the recorded maternal electrocardiograms and compared with birthweight and z‐scores of birthweight adjusted for gestation and gender. Results Data from 5655 women were included. MHR increased from 84.6 bpm at 20–24 weeks to 88.3 bpm at 34+ weeks. Increasing MHR from 70–80 to 80–90 and 90–100 bpm at 20–24 weeks was associated with increasing birthweight from 2940 to 2998 and 3032 g, respectively (P