Umbilical artery velocity waveforms are not valid indices for assessing growth retardation in utero

Blood flow velocity waveforms from the umbilical artery of 126 normal fetuses with no complications at 20-41 weeks and in 31 growth-retarded fetuses, were recorded using pulsed Doppler ultrasound. A total of 140 examinations were performed on normal fetuses and 49 on growth-retarded fetuses. The resistance index (RI) was used as an index of blood flow resistance. In 30 of the 31 growth-retarded fetuses (96.8%), the values of RI were within the mean +/- 2 S.D. of normal fetuses. Placental/fetal weight ratio (P/F ratio) was assessed. All values of P/F ratio of growth-retarded fetuses were within the mean +/- 2 S.D. of normal values. Small placentas expressed as a normal P/F ratio almost always associated with normal RI values. Therefore, measurement of RI on umbilical artery blood flow velocity waveform by Doppler ultrasound cannot serve as a valid diagnostic index to predict growth retardation of the fetus in utero.