Comparison of umbilical artery flow velocity waveform indices as measured by continuous wave Doppler ultrasound.

This study examines four methods, automated and manual, of calculating the pulsatility index (PI) of fetal umbilical artery flow velocity waveforms (FVW) and compares these values to the resistance index (RI), the A/B ratio, and the degree of absence of end diastolic frequencies. The FVWs were obtained by the Doptek continuous wave Doppler ultrasound. All of the maximum envelope indices had significant correlations; a highly significant difference was found between the automated and the manual methods of determining PI. When PI was measured manually, there was a better correlation between the A/B ratio, RI, and degree of absence of end diastolic frequencies than when the automated methods were used.