Does hypercapillarization influence the branching pattern of terminal villi in the human placenta at high altitude?

This study tests the hypothesis that exposure of the placenta to hypobaric hypoxia at altitude results in an altered branching pattern of the villous tree. Histological material from 20 term placentae delivered at altitudes over 3000 m was compared with matched controls from 500 m. Estimates of the mean star volume of intermediate and terminal villous domains were 1.40 x 10(6) microns3 (s.d. 0.63) in the high altitude group and 1.90 x 10(6) microns3 (s.d. 0.34) in the controls (F = 9.07, P < 0.005). The volume fraction of the villous tree occupied by trophoblastic bridges and syncytial knots was 8.1 per cent (s.d. 3.5) in the high altitude group and 3.2 per cent (s.d. 1.6) in the controls (F = 29.45, P < 0.0001). Previous studies have shown that the majority (80 per cent) of bridges are artefacts caused by the plane of section passing tangentially through the trophoblast layer at points of villous bending or branching. The results are, therefore, consistent with the hypothesis that peripheral villi are shorter, knob-like protrusions at high altitude, clustered more closely together. This modified branching pattern was confirmed by scanning electron microscopy. The change in architecture may be due to enhanced angiogenesis stimulated by the lower partial pressure of oxygen prevailing at high altitude.