The aim of this study was to investigate the changes in the number of vessels within tertiary stem villi and intermediate/terminal villi Which may be responsible for the abnormalities in placental vascular resistance and Doppler velocity index values in growth-restricted fetuses. The placentas of 20 cases with intrauterine growth restriction and 30 cases Which Were appropriate for gestational age Were Studied. The umbilical artery resistance index, pulsatility index and systolic to diastolic ratio Were Measured in each case. The vessels Were quantified by a stereological method described previously and vascular surface density and the volume portion of the villi Were calculated. The placentas of preterm and term cases With intrauterine growth restriction displayed significant reductions in the vascular surface density of stem and intermediate/terminal villi and volume portion of intermediate/terminal villi stroma Mien compared Both gestation-matched normally grown cases (p<0.05). There was no significant correlation between Doppler index values of the umbilical artery and the stereological parameters of the intermediate/terminal and stem villi in the intrauterine growth restriction group (p>0.05). Some of the pregnancies with intrauterine growth restriction (six patients) with normal Doppler flow velocity waveforms had reduced vascularization in the placentas. and these pregnancies Were found to have no perinatal complications. We conclude that. although the placental villi show reduced vascularization in pregnancies with intrauterine growth restriction, the Doppler indices may be normal and this normal flow pattern is related to reduced complication rate. Copyright (C) 2002 John Wiley Sons, Ltd.