Effects of low maternal heart rate on fetal growth andbirthweight.

Abstract

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 34weeks or later (34+weeks). 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. Data from 5655 women were included. MHR increased from 84.6bpm at 20-24weeks to 88.3bpm at 34+weeks. Increasing MHR from 70-80 to 80-90 and 90-100bpm at 20-24weeks was associated with increasing birthweight from 2940 to 2998 and 3032g, respectively (P<0.05). MHR and HRV contributed 29% to the variability associated with birthweight, whereas maternal body mass index at recruitment contributed 44%. Similar associations were observed for MHR at 34+weeks. The observed association of low maternal heart rate with birthweight might help to identify pregnancies at risk of poor fetal growth.