Objective: To compare changes in Doppler ultrasound studies of fetal circulation in normal pregnancies with those of a group of preeclamptic patients both with and without intrauterine growth retardation and to demonstrate the best index for predicting adverse perinatal outcome or IUGR. Study design: A cross-sectional study was performed on 125 normal pregnancies and 62 preeclamptic patients at 31-40 weeks of gestation. The umbilical artery systolic-diastolic ratio (UA S/D), UA pulsatility index (PI), the middle cerebral artery (MCA) PI, and the ratio of MCA PI to UA PI were measured. The mean values of the Doppler indices were compared. Different cut-off values (mean+/-2 S.D.) were used for the 31st-35th and the 36th-40th weeks. Results: Significant differences were found between normal pregnancies and preeclamptic patients without IUGR using the mean MCA PI and the MCA PI/UA PI ratio. In the preeclamptic patients with IUGR, all the mean Doppler indices were different from those of the normal pregnancies. In the preeclamptic patients with IUGR the values were different from the preeclamptic patients without IUGR, except for the MCA PI at 31-35 weeks. The UA S/D had the highest sensitivity (88%) and diagnostic accuracy (94%) in predicting the adverse perinatal outcome. The MCA PI/UA PI ratio showed the highest predictive value in determining IUGR by a sensitivity of 84% and a diagnostic accuracy of 87%. Conclusion: Both abnormal umbilical Doppler indices and cerebral-umbilical ratio are strong predictors of IUGR and of adverse perinatal outcome in preeclampsia. The MCA PI alone is not a reliable indicator. The combination of umbilical and fetal cerebral Doppler indices may increase the utility of Doppler ultrasound in preeclamptic subjects. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.