Growth restricted placentas show severely reduced volume of villous components with perivascular myofibroblasts

The restricted placental growth in IUGR is associated with a simultaneous weight and volume restriction for the placental villous tree. It is unknown whether the whole villous tree or only specific parts of it are growth restricted in IUGR. In the case of uniform growth restriction of the villous tree, IUGR placentas could be interpreted as symmetrically smaller versions of normal placentas. Otherwise, IUGR placentas would be morphologically, developmentally and, therefore, functionally different from normal placentas.

We investigated ten normal and eleven IUGR placentas with quantitative microscopic techniques. Using immunohistochemical detection of placental myofibroblasts (γ-sm-actin) and foetoplacental endothelium (CD34), we distinguished between more centrally located villi showing the presence of myofibroblasts (contractile villi; C-villi) and more peripherally located villi showing the absence of myofibroblasts (noncontractile villi; NC-villi).

Compared to normal placentas, IUGR placentas showed significantly reduced mean volume of C-villi, but not of NC-villi. The volume of vessels in both, C-villi and NC-villi, was significantly reduced in IUGR. Additional stereologic estimates confirmed the known alterations in the morphology of NC-villi in IUGR.

Our results suggest that IUGR placentas are not just smaller but morphologically (and therefore functionally) different from normal placentas. We propose that the reduced volume of C-villi and vessels in C-villi reflects a developmental disturbance in the formation of C-villi, which are mostly composed of stem villi. As such, key pathological villous alterations in IUGR placentas could begin before the formation of intermediate and terminal villi, possibly already in the late first trimester of pregnancy.