FULL-TERM BIRTH-WEIGHT AND PLACENTAL MORPHOLOGY AT HIGH AND LOW-ALTITUDE

Objective: To study the association between placental morphology and f ull-term birth weight at high and low altitude. Subjects: Twenty norma l pregnant women living permanently at high altitude (3100 m) and 20 n ormal pregnant women living permanently at low altitude (500 m) in Sou thern Saudi Arabia. Method For each subject in the two groups the mean hemoglobin concentration and hematocrit values throughout pregnancy w ere estimated and these were used as indices for maternal hypoxia. Aft er delivery, the birth weight of each fetus was determined together wi th the placental weight. Placentas were then examined histologically u sing sections stained by periodic acid-Schiff and hematoxylin-eosin. T he mean percentages of villi with syncytial knots, cytotrophoblastic c ells and fetal capillaries were determined. Results: The mean hemoglob in concentration and hematocrit values were significantly greater at h igh altitude than at low altitude (P < 0.001 for both). The mean birth weight and placental weight were significantly greater at low altitud e compared to high altitude (P < 0.025 and 0.001, respectively). The p lacentas from high altitude showed histological changes suggestive of placental hypoxia i.e. significant increase in the incidence of syncyt ial knots, cytotrophoblastic cells and fetal capillaries at high altit ude compared to low altitude (P < 0.005, 0.001 and < 0.05, respectivel y). At both high and low altitude the incidences of syncytial knots an d cytotrophoblastic cells showed positive and significant correlations with mean maternal hemoglobin (r = 0.5 and 0.6, P < 0.01 and < 0.001, respectively) and hematocrit (r = 0.5 and 0.6, P < 0.01 and 0.001, re spectively) during pregnancy and negative and significant correlations with fetal birth weight (r = -0.4 and -0.6, P < 0.01 and P < 0.001, r espectively). Conclusion: The low birth weight observed at high altitu de compared to low altitude appeared to be mainly secondary to placent al hypoxia resulting from maternal hypoxia which in turn was caused by high altitude hypoxia. (C) 1997 International Federation of Gynecolog y and Obstetrics.