First trimester development of human chorionic villous vascularization studied with CD34 immunohistochemistry

Normal chorionic villous vascularization is essential for the undisturbeddevelopment of pregnancy. Defective vasculogenesis may play a role inpathological pregnancy. To assess pathological chorionic villousvascularization, normal vascularization has to be defined first. Few dataare available on this topic. The aim of this study was therefore toinvestigate normal chorionic villous vascularization in ultrasound-datedfirst trimester pregnancies from week 5 menstrual age to week 12 (n = 41),using quantitative CD34 immunohistochemistry. Two important processes inchorionic villous vascularization were quantitatively illustrated: (i)maturation, reflected by an increase of the total number of luminizedvessels as opposed to non-luminized haemangioblastic cords and (ii)margination, due to a decrease of villous stromal area and an increase oftotal villous vascular area. The percentage of villous stromal areaoccupied by vascular elements (area difference %) increased from 0.7% inweek 5-2.5% in week 10. Therefore, the area of the villous stroma occupiedby vascular elements increases and the vessels are situated closer to thetrophoblastic layer suitable for fetal-maternal exchange. There was also atrend in increased number of peripheral vessels (2.0 in week 5 to 4.6 inweek 10), supporting both developmental mechanisms. In conclusion, inexactly dated normal human first trimester pregnancies, development of thechorionic villous vascular system seems to be mostly characterized bymaturation of luminized vessels from primitive haemangioblastic cords, andmargination to a situation of peripherally located vessels.