Spectral Analysis of Beat-to-Beat Intervals of the Fetal Heart Obtained by Doppler Ultrasound

Abstract

Fetal heart rate monitoring has been widely used for the early investigation of the fetal outcome in current clinical settings. Interpretation of fetal heart rate tracing is sometimes indecisive, especially when the fetus is premature. In contrast to adults, the frequency analysis of fetal heart rate fluctuations has been unsuccessful. In this study, we succeeded in nonstationary frequency analysis of fetal heart rate fluctuations, using noninvasive Doppler ultrasound to measure beat-to-beat intervals of fetuses. We used an autoregressive method based on a 24-cycle stationarity. A dual peak was observed in the range of 0-0.125 cycles/beat from at least 20 weeks of gestation which increased in the resting state with gestational age. The peak area increased remarkably with fetal movement. The integrated value of the peak area will provide a powerful approach to the understanding of the development of fetal autonomic function and to a new fetal monitoring.