Placental morphometry in pregnancies complicated by intrauterine growth retardation with absent or reversed end diastolic flow in the umbilical artery

The aim of this study was to assess any possible correlation between villous tree architecture and its vascularization, and absent or reversed end-diastolic flow velocity (ARED) in the umbilical artery. The study group included seven pregnancies complicated by IUGR (estimated fetal weight < 10th percentile) and absent end-diastolic flow velocity in the umbilical artery. A gestational-age matched group of seven normally grown pregnancies was selected as control group. At delivery, the placenta was weighed and immersed in 10% neutral buffered formalin. A stratified random sampling procedure was used to obtain 12 blocks of full-thickness tissue per organ. A single random section was cut from each block. The following morphometric parameters were evaluated in each section: mean vessel diameter, volume density of the villous tissue, stem villi and terminal villi. Measurements were performed using a computerized Video Image Analysis system. No significant difference in mean vessel diameter was found between the two groups (37.1 microns versus 36.1 microns; p = 0.1). There was a significant reduction in the proportion of total villous tissue in the ARED group (43% versus 52%): this was due to a significant reduction in the volume of tissue occupied by the terminal villi (14.1% versus 18.4%). No significant difference was found in the proportion of villous tissue occupied by the stem villi (42% versus 40%). Several studies have investigated the anatomical and/or vasomotor bases of absent end diastolic flow velocity in the umbilical artery of fetuses with severe IUGR. Our observations of a significant reduction in the proportion of villous tissue occupied by the peripheral villi are consistent with the theory that failure of normal development of the terminal villous is responsible for the increased vascular resistance in IUGR pregnancies with ARED.