Full-term birth weight and placental morphology at high and low altitude

Objective: To study the association between placental morphology and full-term birth weight at high and low altitude. Subjects: Twenty normal pregnant women living permanently at high altitude (3100 m) and 20 normal pregnant women living permanently at low altitude (500 m) in Southern Saudi Arabia. Method: For each subject in the two groups the mean hemoglobin concentration and hematocrit values throughout pregnancy were estimated and these were used as indices for maternal hypoxia. After delivery, the birth weight of each fetus was determined together with the placental weight. Placentas were then examined histologically using sections stained by periodic acid-Schiff and hematoxylin-eosin. The mean percentages of villi with syncytial knots, cytotrophoblastic cells and fetal capillaries were determined. Results: The mean hemoglobin concentration and hematocrit values were significantly greater at high altitude than at low altitude ( P < 0.001 for both). The mean birth weight and placental weight were significantly greater at low altitude compared to high altitude ( P < 0.025 and 0.001, respectively). The placentas from high altitude showed histological changes suggestive of placental hypoxia i.e. significant increase in the incidence of syncytial knots, cytotrophoblastic cells and fetal capillaries at high altitude compared to low altitude ( P < 0.005, 0.001 and