Placental villus morphology in relation to maternal hypoxia at high altitude

Pregnancy at high altitude is associated with maternal hypoxaemic hypoxia with resultant intervillus blood hypoxia. Maternal haemoglobin concentration and blood gases were measured in pregnant women in two cities in Peru; Lima at sea level (n=18) and Cerro de Pasco at 4300 metres above sea level (n=12). Following delivery, placental sections from both groups were examined histomorphometrically using an image analysis system. Villus diameter, villus cross-sectional area, capillary diameter, capillary cross-sectional area and the percentage of villus cross-sectional area occupied by villus capillaries were calculated and parameters were compared between the two altitude groups. Maternal haemoglobin concentration and maternal blood pH were significantly higher, and maternal pO(2), pCO(2)and O(2)saturation were significantly lower in the high altitude group compared to those at sea level. The villus vessel area as a percentage of villus cross-sectional area and capillary diameter were significantly greater in the cases from the high altitude group and villus vessel area as a percentage of the villus cross-sectional area was significantly related to maternal pO(2)(r=-0.7, P=0.01), and maternal pCO(2)(r=0.7, P=0.02), but multiple regression analysis demonstrated that only pO(2)remained significantly independently associated with these villus histological findings (P=0.03). Placental terminal villi from term pregnancies at high altitude show different morphological features from pregnancies at sea level, and these changes are primarily related to maternal pO(2). The predominant morphological alteration is an increase in villus capillary diameter and therefore of the proportion of villus cross-sectional area occupied by capillary lumens.