Respiratory sinus arrhythmia in the human fetus.

This study explores the relationship between fetal heart rate variability and fetal breathing movements in the term fetus. Fourier analysis was applied to fetal heart rate variability during fetal breathing and nonbreathing episodes. A distinct component in the order of 0.7 to 0.95 Hz was demonstrated in fetal heart rate variability during breathing episodes. These frequencies have the same distribution as the corresponding rate of breathing and therefore indicate that respiratory sinus arrhythmia exists in the term fetus.