Background: Intrauterine growth restriction (IUGR) is an obstetric syndrome with a high incidence and severe health burden. The restricted placental growth in IUGR reflects a weight restriction for the placental villous tree. It is unknown whether the whole villous tree or only specific parts of it show restricted growth in IUGR. Clarifying this would have a significant impact on the development of innovative therapeutic approaches for compensating placental dysfunction in IUGR since in the case of uniform growth restriction of the villous tree, IUGR placentas would primarily be smaller than normal placentas. However, if only specific parts of the villous tree are growth restricted, then IUGR placentas would be morphologically, developmentally and, therefore, functionally different from normal placentas. Methods: We investigated ten normal placentas and eleven IUGR placentas with quantitative microscopic techniques (design-based stereology). 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). Findings: Compared to normal placentas, IUGR placentas showed significantly reduced mean volumes of C-villi and vessels in C-villi but not of NC-villi. Additional stereologic estimates confirmed the known alterations in the morphology of NC-villi in IUGR. Interpretation: Our results suggest that IUGR placentas are not just smaller but morphologically (and therefore functionally) different from normal placentas. We hypothesize that the reduced volume of C-villi and vessels in C-villi reflects a developmental disturbance in the formation of C-villi (most of them being stem villi). As such, key pathological alterations in IUGR placentas could begin before the formation of intermediate and terminal villi, possibly already in the late first trimester of pregnancy. Funding Statement: Supported by the German Research Council (DFG Fr1245/9-1, to HGF). Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The ethics board of Ludwig-Maximilians-University of Munich (LMU Munich) approved all investigations under the numbers 084-11 and 478-12.
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