[Reference values for the pulsatility index and the resistance index of blood flow curves of the umbilical artery and fetal aorta in the 3d trimester].

In 209 pregnancies without complications we recorded blood velocity waveforms of the umbilical artery and the foetal aorta between 29 and 42 weeks of gestation by means of a Duplex-pulsed Doppler system (umbilical artery: n = 276; foetal aorta: n = 244). We calculated the pulsatility index (PI) and the resistance index (RI). Both indices were normally distributed. The regression lines and reference ranges for the 95% confidence intervals are shown. The PI as well as the RI of waveforms of the umbilical artery demonstrated a significant fall with increasing gestation. The PI of the foetal aorta demonstrated a gentle, non-significant fall; RI showed no changes throughout the third trimester. Comparisons with the reference ranges published by other authors are discussed.