Histomorphometric characterisation of shared and non-shared villus territories in monochorionic (MC) twin placentae

Abstract

Flow and physiological data suggest there is reduced flow in shared vs. non-shared cotyledons. We hypothesised that there are histomorphometric differences in terminal villus architecture in MC twins. Placentae from uncomplicated MCDA twins and those discordant for IUGR and twin–twin transfusion syndrome (TTTS) were injected immediately after delivery to demonstrate vascular anastomoses and immersion-fixed. Tissue blocks taken from representative areas of shared and non-shared cotyledons were analysed histomorphometrically by image analysis software. Fifty terminal villus cross-sections were examined from each block of co-twin territory and shared cotyledons. Villus diameter, villus cross-sectional area, capillary diameter, capillary cross-sectional area and the percentage of villus cross-sectional area occupied by villus capillaries were calculated and parameters were compared between the groups. In the uncomplicated MCDA twins, the terminal villi in the normal cotyledons of the smaller twins had significantly fewer, smaller capillaries compared to the shared and normal cotyledons of the larger twins. In those complicated by TTTS and discordant for IUGR, the terminal villi in the shared cotyledons had significantly fewer and smaller capillaries compared to the normal cotyledons of the smaller and larger twins. This is consistent with reduced flow rate in the shared cotyledons compared to the normal cotyledons.