The branching pattern of villous capillaries and structural changes of placental terminal villi in type 1 diabetes mellitus

Maternal diabetes is associated with changes of the placental structure. These changes include great variability of vascularity manifested by strikingly hypovascular as well as hypervascular terminal villi. In this paper, normal placental terminal villi and pathological villi of type 1 diabetic placentas were compared concerning the structure of villous stroma, spatial arrangement of villous capillary bed and quantitative assessment of capillary branching pattern. Formalin fixed and paraffin embedded specimens of 14 normal and 17 Type 1 diabetic term placentas were used for picrosirius staining, vimentin and desmin immunohistochemistry and confocal microscopy. 3D models of villi and villous capillaries were constructed from stacks of confocal optical sections. Hypervascular as well as hypovascular villi of diabetic placenta displayed changed structure of villous stroma, i.e. the collagen envelope around capillaries looked thinner and the network of collagen fibers seemed less dense. The desmin immunocytochemistry has shown that stromal cells of hypervascular as well as hypovascular villi appeared nearly or completely void of desmin filaments. In comparison with normal villi, capillaries of hypovascular villi had a smaller diameter and displayed a markedly wavy course whereas in hypervascular villi numerous capillaries occurred in reduced stroma and often had a large diameter. The quantitative assessment of capillary branching has shown that villous capillaries are more branched in diabetic placentas. It is concluded that type 1 maternal diabetes enhances the surface area of the capillary wall by elongation, enlargement of diameter and higher branching of villous capillaries and disrupts the stromal structure of terminal villi.