Umbilical artery velocity waveforms: normal reference values for A/B ratio and Pourcelot ratio

Abstract

Normal reference values for the umbilical artery Pourcelot ratio and A/B ratio are reported. Thirty-five normal patients were studied serially from 20 weeks to term. The A/B ratio centiles were corrected for non-normality of the underlying distribution by transforming from the Pourcelot ratio values. The correction needed was small during the last trimester, but larger for second trimester data. Of the 35 patients 24 nulliparous and there was a slight tendency for the waveform indices to be higher in the nulliparae, but the numbers in this study were too small to be conclusive about the effect of parity.