Fig. 3

Prenatal time trends of HRV parameters in murine and human embryos/fetuses. Time trends using linear mixed models corrected for mean embryonic/fetal heart rate and sex are provided separately for all HRV parameters. The dotted lines indicate 95% confidence intervals (CI) and the black dots indicate the raw data points. A–E HRV parameters in mouse embryos. A In mouse embryos, mean heart rate increased throughout gestation. B, C SDNN consistently low, whereas RMSSD demonstrated a slight decreasing trend. This suggests that, although a trend towards a decrease in parasympathetic activity during development was observed, definitive establishment of cardiac autonomic function is not yet observed. D The SDNN/RMSSD ratio remained predominant to RMSSD (i.e. ratio < 1), but increased in favor of SDNN throughout gestation. E pNN10 showed no specific trend. F–J HRV parameters in human fetuses. F In human fetuses, mean heart rate decreased throughout gestation. G–H SDNN and RMSSD increased from 20 to 30 WGA, suggesting that cardiac autonomic activity (mainly parasympathetic activity) establishes at approximately 20 WGA and matures until 30 WGA. I The SDNN/RMSSD ratio remained predominant to RMSSD (i.e. ratio < 1), demonstrating predominant vagal control throughout pregnancy. J pNN10 increased with gestation, which illustrates that vagal effect intensified throughout gestation. F–J are modified and extended after Zwanenburg et al. [30], published open access under Creative Commons Attribution License (CC BY)