[Studies on the periodicity of fetal and neonatal heart rate variability by fast Fourier transform analysis]

Heart rate changes were analyzed by fast Fourier transform technique in 68 normal fetuses of 23 to 41 weeks, 8 normal deliveries, 11 normal neonates, cases of fetal heart rate late deceleration, sinusoidal pattern, and anencephalic fetus. High spectral densities were noted at 0.02 to 0.12 Hz in inactive phases of normal fetuses, whereas they were 0.2 to 0.4 Hz in active phases. The densities were particularly high at 0.64 to 0.8 Hz in normal neonates. An anencephalic fetus and a case of late deceleration showed high spectral densities at 0.02 to 0.12 Hz. These results suggest that fetal heart rate is controlled basically by 8 sec or greater periodicity. Neonatal 1.3 to 1.6 sec periodicity suggests a relationship between heart rate and respiration. No change in periodicity was found in fetal heart rate after the administration of 0.5 mg of atropine sulfate to the mother in 12 cases.