Morphometric assessment of the oxygen diffusion conductance in placentae from pregnancies complicated by intra-uterine growth restriction

The morphometric oxygen diffusive conductance (D-p) of the placenta provides a measure of the efficiency of oxygen transfer between the mother and the developing fetus. Any change in the D-p may point towards possible adaptation in the light of altered oxygen transfer. Placentae from normal (n=40) and small for gestational age SGA (n=24) pregnancies were analysed using stereological techniques. Each placenta was uniform randomly sampled and tissue samples processed to wax infiltration and embedding using conventional histological preparatory methods. A combination of stereological techniques and physiological constants were used to estimate the partial conductances across the five major tissue compartments involved in oxygen transfer. There was a significant reduction in both fetal birthweight and placental weight in the SGA group when compared with controls. A decrease in both chorionic (S-cv) and fetal capillary (S-fc) surface area was also observed in SGA placentae when compared with,controls (P>0.001). Villous membrane harmonic thickness (T-vm) was reduced in the SGA placentae (2.33 mum) when compared with controls (2.67 mum P=0.019). This resulted in a reduction in the minimum D-p in SGA placentae when compared with controls (P=0.023). Adjusting for fetal weight resulted in no difference in the specific diffusive conductance. Changes in T-vm in SGA placentae combined with changes in basic surface areas were insufficient to maintain overall D-p values comparable with control placentae. (C) 2003 Elsevier Science Ltd. All rights reserved.