Structural differences of normal and abnormal terminal villi in diabetic placenta

Placental terminal villi contain the overwhelming majority of placental capillaries. Normal structure of terminal villi, i.e. normal organization of trophoblast, capillaries and stroma, ensures the efficiency of materno-fetal transport. Small amount of terminal villi displaying abnormal structural features may occur in normal placentas, but higher ratio of such villi is typical for placentas associated with complicated pregnancies, first of all with maternal diabetes. In diabetic placentas, abnormal villi may display signs of maturation disorders, edema, stromal fibrosis, excessive number of syncytial knots and variable villous vascularity. Here are compared some structural characteristics of normal placental terminal villi and abnormal placental terminal villi found in diabetic placentas.

The study using confocal microscopy has shown that terminal villi in normal placentas are slender and longer than those in diabetic placentas. As they are complementary to the intervillous space, their shape different from the normal ones changes dimensions of slits of intervillous space among them. Capillaries of normal villi are organized parallel to the long axis of villus and form together with trophoblast vasculosyncytial membranes. The changed arrangement of capillary bed in diabetic villi demonstrates itself in two forms. The former looks hypovascularized and is characterized by markedly waved thin capillaries. Due to their shape, vasculosyncytial membranes are less observable. The latter looks hypervascularized and displays capillaries of strikingly large diameter and wavy course. Large vasculosyncytial membranes and syncytial knots are observed.

In last trimester of pregnancy, the placental growth and development it characterized mainly by growth of terminal placental villi and their capillary bed. Immunocytochemical detection of Ki67 antigen has revealed that the Ki67 positive nuclei are found in normal villi in all cellular compartments, i.e. trophoblast, stroma and capillary wall, whereas both types of abnormal villi show conspicuously lower frequency of those nuclei.

Stromal cells support villous architecture and produce extracellular matrix. As shown by desmin immunocytochemistry,their projections are in very tight relationship to the capillary wall and demarcate stromal channels in normal villi. Both the hypo- and hypervascularized villi are very poor in those cells.

Our findings make evident that the abnormal forms of placental terminal villi may change conditions of the maternal blood circulation in their neighborhood, that a kind of disturbed angiogenesis produces abnormal villous capillary bed, that the cells of such villi display decreased proliferation potential, and that their stromal architecture is disrupted. The presented results suggest that higher ratio of those villi may impair placental function and thus threaten fetal well being.

Supported by PRVOUK P25/LF1/2.