Seventy-five high-risk pregnancies were studied in order defineto the clinical value of the analysis of fetal blood flowvelocity waveforms in early screening for growth retarda-tion. Recordings were obtained at 26–28 weeks' gestation, inthe absence of ultrasonographic signs of growth retardation, using a pulsed duplex Doppler system. The pulsatility indexwas evaluated a t the level of the umbilical artery, descend-ing aorta, and internal carotid artery. Fetuses (N = 23) whodeveloped growth retardation showed higher values ofpulsatility index in the umbilical artery (P < .001) anddescending aorta (P < .05) than fetuses of normal growth. Inthe internal carotid artery, the pulsatility index was lower (P < .001) in the fetuses who developed growth retardationthan in those with normal growth. The ratio between thepulsatility indexes of the umbilical and internal carotidarteries proved an accurate predictor of growth retardation(specificity 92.3%; sensitivity 78.2%; positive predictivevalue 81.8%; negative predictive value 90.5%; accuracy 88%).