A study of biorhythm using a power spectral analysis on the fluctuation in fetal and maternal beat-to-beat intervals

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Six normal fetuses and expectant mothers in the third-trimester pregnancy and seven IUGR fetuses were studied. In the normal group, the mother and the fetus were monitored simultaneously, while in IUGR group only the fetus was monitored continuously for the period of 24 hours on a beat-to-beat basis. A power spectrum analysis was carried out on the fluctuations in fetal beat-to-beat intervals. Over the period of 24 hours, an LF area, integrated low frequency domain (0.025-0.125 cycle/beat), was calculated for every ten minutes, and the average of six LF areas was defined as the LF area for the hour. By plotting these 24 average LF areas obtained for one day, a curve showing the fluctuations in LF areas over the period of 24 hours was drawn. To detect periodic components of a fetal rhythm of the fluctuations in one day, a spectral analysis was carried out on the fluctuations of hourly fluctuation. Then, rhythms of the fluctuations in LF areas were detected by using the cosinor method. In the mother same procedure was performed to identify periodic components.A 12-hour-period rhythm and a 24-hour-period rhythm were found in the activities of the autonomic nervous system of the normal fetuses. In IUGR fetuses, these rhythms were not observed because of the small amplitude. A 12-hour-period rhythm was not observed in the mother.Fetal rhythms of 12 hours cycle in autonomic activity seems to be characteristic, which was not observed in the mother.