Stereological Investigation of Placental Morphology in Pregnancies Complicated by Pre-eclampsia with and Without Intrauterine Growth Restriction

The aim of this study was to quantify placental morphology in pregnancies complicated by pre-eclampsia with and without intrauterine growth restriction. Particular attention is given to the dimensions and composition of peripheral (intermediate+terminal) villi. Placentae from 9 control pregnancies, 5 cases of pre-eclampsia, 5 cases of intrauterine growth restriction and 5 cases of pre-eclampsia with intrauterine growth restriction were randomly sampled for location and position. Formalin-fixed, wax-embedded sections stained by the Masson trichrome method were subjected to stereological analysis in order to quantify the volumes of placental components and the surfaces and derived diameters for peripheral villi and fetal capillaries. Group comparisons were drawn using two-way analysis of variance. Fetal weights were reduced in all complicated pregnancies but only intrauterine growth restriction was accompanied by a significantly smaller placenta. Pre-eclampsia was not associated with main effects on placental morphology and (except for trophoblast thickness) there were no interaction effects involving pre-eclampsia. In contrast, intrauterine growth restriction was associated with a placenta which had reduced volumes of intervillous space and all types of villi (stem, intermediate, terminal). The impoverished growth of peripheral villi affected all tissues (trophoblast, stroma, capillaries) and was accompanied by smaller exchange surface areas and a thicker trophoblastic epithelium. The derived mean diameters of villi and capillaries were not affected. It is concluded that intrauterine growth restriction, but not pre-eclampsia, is associated with substantial changes in placental morphology including impoverished growth of villi and fetal vasculature. These changes are likely to reduce placental oxygen diffusive conductances and contribute to fetal hypoxic stress.