Umbilical and uterine artery flow velocity waveforms. Effect of the sampling site on Doppler ratios.

Pulsed Doppler duplex sonography was performed on 58 patients in order to determine whether Doppler ratios of umbilical and uterine artery flow velocity waveforms vary with the site at which measurements are taken along their respective arterial beds. Umbilical artery ratios were significantly higher at the fetal end of the cord when compared to ratios at the placental cord insertion. In the maternal circulation, ratios from arcuate artery waveforms were lower than those obtained from the uterine artery. This site-dependent difference in ratios could be clinically important when studying ratios from the umbilical artery. Accuracy of Doppler measurements in the individual patient and in scientific investigations may be improved if uniform measurement techniques are used.