[Human placenta structure in II and III trimesters of physiological pregnancy]

The placenta of 20 women with normal pregnancy was studied during II and III trimesters to obtain the complex characteristic of the structures participating in the formation of syncytio-capillary membranes. Immunocytochemical endothelial cell marker CD34 and morphometry were used for the assessment of some villous parameters: villous area, villous stromal area, villous epithelial area and vascular endothelium area. The main attention was given to the remodeling of the villous epithelium and capillary network. The significant reduction of the epithelial area and that of the villous stroma was detected simultaneously with intensive their vascularization. Morpho-functionally, most of the terminal villi were specialized, containing sinusoid-type capillaries which were in close contact with attenuated, anuclea regions of syncytiotrophoblast. The proportion of terminal villous endothelium in respect to the stroma was significantly increased. Thus, in II and III trimesters of physiological pregnancy the structural changes take place in the placenta, in particular, the capillaries are transformed into thin-walled sinusoids, that approach and closely interact with syncytiotrophoblast resulting in the formation of the syncytio-capillary membranes necessary for an adequate diffusion and meeting the growing needs of the fetus.