A comparison of episodic heart‐rate patterns in the fetus and newborn

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Abstract
Fourier analysis was applied to episodes of high and low heart rate variation in the near-term fetus. The spectral densities of the variations in pulse intervals from 1 to 7 cycles/min were almost identical with those found in the newborn infant during both active and quiet sleep. A computer program, designed to separate low and high heart rate variation episodes in the fetus, identified 7 of the 8 quiet sleep episodes in 4 infants. None of the other neonatal behavioral states had low heart rate variation. There is increasing, although indirect, evidence that low heart rate variation episodes indicate quiet sleep in the human fetus near term.