FIRST-TRIMESTER DEVELOPMENT OF HUMAN CHORIONIC VILLOUS VASCULARIZATION STUDIED WITH CD34 IMMUNOHISTOCHEMISTRY

Normal chorionic villous vascularization is essential for the undistur bed development of pregnancy, Defective vasculogenesis may play a role in pathological pregnancy, To assess pathological chorionic villous v ascularization, normal vascularization has to be defined first, Few da ta are available on this topic, The aim of this study was therefore to investigate normal chorionic villous vascularization in ultrasound-da ted first trimester pregnancies from week 5 menstrual age to week 12 ( n = 41), using quantitative CD34 immunohistochemistry. Two important p rocesses in chorionic villous vascularization were quantitatively illu strated: (i) maturation, reflected by an increase of the total number of luminized vessels as opposed to nonluminized haemangioblastic cords and (ii) margination, due to a decrease of villous stromal area and a n increase of total villous vascular area, The percentage of villous s tromal area occupied by vascular elements (area difference %) increase d from 0.7% in week 5-2.5% in week 10, Therefore, the area of the vill ous stroma occupied by vascular elements increases and the vessels are situated closer to the trophoblastic layer suitable for fetal-materna l exchange, There was also a trend in increased number of peripheral v essels (2.0 in week 5 to 4.6 in week 10), supporting both developmenta l mechanisms, In conclusion, in exactly dated normal human first trime ster pregnancies, development of the chorionic villous vascular system seems to be mostly characterized by maturation of luminized vessels f rom primitive haemangioblastic cords, and margination to a situation o f peripherally located vessels.