Histomorphometry of the human placenta in Class B diabetes mellitus.

Different morphometric parameters have been applied to the study of the morphological differences between a group of normal placentae and a group of placentae collected from Class B diabetic mothers. The placentae of the diabetics were divided in two groups based on the growth characteristics and neonatal outcome of the infants at birth. It has been shown that the placentae of the appropriate for gestational age infants were morphologically very similar to the control group except for a well-developed villous vascularization. In contrast, the placentae of the large for gestational age infants were shown to differ from the controls by having heavier placentae due mainly to a significant accumulation of non-parenchyma and a moderate increase in parenchymal tissue. Consequently, although there was significantly more villous tissue in these placentae, the surface areas of exchange between mother and fetus in terms of capillary and villous surface areas were only moderately enlarged due to a relatively lower number of villi containing non-parenchymal tissue. However, on a functional basis, despite these morphological differences, the results of this study suggest that placental function is not adversely affected in Class B diabetics, and the perinatal morbidity associated with this condition is probably the result of metabolic abnormalities present in the mother and the fetus.