Fetal heart rate, heart rate variability, and heart rate/movement coupling in the Safe Passage Study

Objective: To determine normative values for heart rate patterns in healthy fetuses. Methods: This research is from the Safe Passage Study conducted by the Prenatal Alcohol and SIDS and Stillbirth (PASS) Network. A standardized protocol assessed fetal heart rate (FHR), heart rate variability (HRV), and movement from 1655 fetuses at three-time points during gestation (20–24 weeks, 28–32 weeks, 34–38 weeks gestation). Results: FHR decreased while HRV increased over gestation. At the latter two ages, males had significantly lower FHR than females while there were no sex differences in FHR at 20–24 weeks. When accounting for the fetal state during late gestation (34–28 weeks), we found that males had significantly lower FHR than females in the active fetal state only. Conclusion: Results demonstrate significant state, gestational age, and sex-related changes in cardiac activity, somatic activity, and autonomic function as the fetus approaches birth.