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