Fetal microcirculation of abnormal human placenta. I. Scanning electron microscopy of placental vascular casts from small for gestational age fetus.

The latex injection-corrosion cast technique coupled with scanning electron microscopy was applied to the study of small for gestational age placentas. The main ultrastructural changes observed in the fetal vasculature of small for gestational age placentas were less branching of arteries and veins, capillaries with variable diameters, and many capillary bud projections; also numerous "H"-shaped anastomoses were present in the capillary network. The corrosion/cast technique approach enabled us to visualize the three-dimensional distribution of arteries, veins, and capillary network as well as the ultrastructural alterations among the various-sized vessels in the abnormal placenta. Light microscopic examination of these placentas revealed numerous syncytial knots and fibrinoid deposits pressing on arteriolar and capillary vessels at different locations. We suggest that the numerous capillary buds and anastomoses are characteristics of neovascularization and may be a compensatory phenomenon of the capillary network. This information could shed new light on alterations of physiologic functions of the pathologic placenta.