Patterns of villous and intervillous space growth in human placentas from normal and abnormal pregnancies

To apply a new stereological approach (relating an exponent of villous surface to volume) to test for patterns of change in placental villi and intervillous space from normal and abnormal pregnancies.

Placentas from normal gestation and pregnancies associated with hypoxic stress (high altitude, diabetes, cigarette smoking) were sampled randomly, fixed in formalin and embedded in paraffin wax for stereological analysis. Volumes (villi, intervillous space) were estimated by point counting and surface areas (villi) by intersection counting. A dimensionless coefficient (S3/2/V) was then calculated to test for isomorphic changes. Comparisons within groups were drawn using analysis of variance.

Changes in villi were isomorphic at high altitude and in placentas from women who smoked during pregnancy. The same pattern is seen in placentas associated with preeclampsia. Changes during gestation and diabetes are anisomorphic, i.e. villous surface area alters disproportionately to volume. A similar pattern is seen in maternal anaemia. Alterations in the intervillous space were isomorphic in diabetes and smoking but anisomorphic during gestation, at high altitude and in maternal anaemia and pre-eclampsia.

The approach has advantages over alternatives (star volume and topological analysis). Structural changes influence placental transport and haemodynamics but there are subtle differences between groups which may depend on the nature of the hypoxic stress and the adaptations made by individual tissue compartments.