Objective: Our purpose was to determine the morphometric diffusing capacity of the human placental villous membrane in cases of maternal iron-deficiency anemia.
Study design: Material from 10 term placentas from mothers with hemoglobin levels < 10 gm/100 cm3 was compared stereologically with control material from women with normal hemoglobin concentrations matched for age and parity. Data were compared with Student t test.
Results: Birth and placental weights were constant between the two groups. Maternal anemia was associated with a significant reduction in both volume and surface area of intermediate and terminal villi (157.8 vs 234.5 cm3 and 9.5 vs 14.9 m2, respectively). There was a concomitant rise in the volume of pathologic areas (32.1 vs 4.1 cm3). Harmonic mean thickness of the villous membrane was significantly less in the anemia cases (5.86 vs 7.15 microns), because of an increase in volume fraction of the fetal capillaries. Consequently, the morphometric diffusing capacity of the villous membrane was maintained (4.49 vs 5.31 cm3.min-1.mm Hg-1, t = 1.04, p > 0.05).
Conclusions: There is a reduction rather than an enlargement of the placental villous tree in cases of maternal anemia. This may be because of underlying malnutrition. Nonetheless, the placenta adapts through thinning of the villous membrane so that diffusing capacity is maintained at normal levels.