Quantitative characterization of villous capillary branching in diabetic placentas

Introduction: Maternal diabetes mellitus is associated with adverse consequences to mother and baby. In the placenta, the only organ mediating the effects of a changed maternal environment on the fetus, maternal diabetes manifests itself by changed placental structure. The microscopic picture encompasses among other great variability in peripheral villous vascularity showing both normal vascularization, hypovascular as well as strikingly hypervascular villi. Stereological studies of total capillary volumes and surface areas have shown discrepant results. Studies on the spatial arrangement of villous vascular bed are sparse and inconsistent.

Aim: To investigate differences in spatial organization and density of the capillary bed in peripheral villi, normal and diabetic placentas were analyzed.

Material and Methods: Placental specimens were collected by systematic random sampling from 14 normal, 11 GDM (= gestational diabetes) and 16 DMI (= type I diabetes) placentas. Tissue samples were fixed in formalin with admixture of eosin, and embedded in paraffin. Sections cut at 120 µm from randomly chosen seven blocks per placenta were analyzed by a confocal laser scanning microscope Leica SPE. Fifteen fields of view per section were sampled in a systematic uniform random manner and examined in well-developed terminal villi which were lying completely inside the thick section. The topology of capillaries was analyzed by the method of topological schemes. The frequency of variable types of capillary bed found in studied groups was statistically analyzed. Stacks of optical sections recorded by a confocal microscope were used for both the visualization of villous capillaries by 3D reconstruction, and visualization of mutual relationships of villi in the intervillous space by the maximal projection method.

Results: These two simplest forms of villous capillary bed were U-like loops and three longitudinally oriented capillary segments confluent near the tip of villus. Beds consisting of four or more longitudinal capillaries occurred rarely, but were more frequent in diabetic villi. Some villi had capillary segments interconnected with one or more redundant connections´ (RC), i.e. capillaries that could be removed without disconnecting the capillary bed. The analysis of topological schemes showed that the proportion of villous capillary beds without RCs was higher in normal placentas (80%) than in GDM (61%) and DMI (66%) placentas respectively. In both groups of diabetic placentas the mean number of RCs per villus was significantly higher (0.49 in GDM group, 0.43 in DM I group) than in the control group (0.23). In some GDM placentas, but in particular in the DMI placentas were observed abnormal villi of conspicuously larger size with edematous stroma and few capillaries. In addition, the villi in some DMI placentas displayed chorangiosis. 3D reconstruction of those villi showed a markedly waved capillaries of highly variable diameter forming dense capillary bed. As shown by the maximal projection method, the arrangement of capillaries in such villi influences their size and shape, which results in changes in the shape and dimensions of the adjoining parts of the intervillous space.

Conclusions: In order to compensate maternal metabolic disorder, the diabetic placenta manifests more intense placental angiogenesis, which results in both a denser villous capillary bed and abnormalities in spatial arrangement. The consequent changes in the shape and size of the villi may influence the microrheological conditions of the maternal blood flow in the intervillous space.

Supported by the GACR 304/09/0733.