AbstractObjectiveTo evaluate the distribution of Doppler pulsatility index (PI) measurements of the umbilical and middle cerebral arteries in singleton fetuses of women with normal uterine artery blood flow and to construct reference ranges for the cerebroplacental PI Doppler ratio.MethodsThe PI was determined in the mid‐portion of the umbilical artery and the mid‐ or distal segment of the middle cerebral artery in 306 normal singleton fetuses. The cerebroplacental Doppler ratio (CPR) was determined from paired measurements. After determination of the best fit, reference ranges were constructed for each parameter against gestational age (GA).ResultsThe PI for the umbilical artery had a linear relationship with GA (umbilical artery PI = − 0.0246 × GA + 1.7791, r2 = 0.4025, P < 0.001). The middle cerebral artery PI and the CPR both showed a quadratic relationship with GA (middle cerebral artery PI = − 0.0058 × GA2 + 0.3335 × GA − 2.7317, r2 = 0.2365, P < 0.01), (CPR = − 0.0059 × GA2 + 0.383 × GA − 4.0636, r2 = 0.2788, P < 0.001).ConclusionThe CPR is not constant throughout gestation. Reference ranges constructed by a standardized Doppler technique may be of benefit in the monitoring of high‐risk pregnancies. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.