Doppler evaluation of fetal hemodynamics.

Human umbilical hemodynamics was investigated in 27 pregnant patients with gestational ages from 29 to 43 weeks using a pulsed Doppler flowmeter. The signals were analyzed by Fast Fourier Transform using a minicomputer. Coherent averaging of the signals, along with the computation of maximum velocity, mean velocity and the first moment of Fourier spectra about the zero frequency axis were performed. Hemodynamic indices were measured utilizing a comprehensive feature characterization technique of the blood flow velocity waveform. It was observed that coherent averaging reduced spectral variance thus relatively simplifying the analyses. The Pulsatility Index based on the first moment of the Fourier spectra indicated a higher umbilical flow change during the fetal cardiac cycle, than that predicted by the peak velocity Pulsatility Index. We also observed a high Pulsatility Index in association with three cases of oligohydramnios indicating the possibility of an elevated placental circulatory impedance. Variation in the peak velocity up to 20% was also noted with fetal breathing movements. Further studies are necessary to determine the clinical relevance of these findings.