Infant birth weight is related to maternal arterial oxygenation at high altitude.

Infant birth weight is reported to decrease at high altitude as a reulst of fetal growth retardation (McCullough, Reeves, and Liljegren. Arch. Environ, Health. 32: 36--39, 1977) but not all babies born at high altitude are small. We hypothesized that maternal characteristics acting to lower arterial O2 content would contribute to smaller infant birth weight. To test this hypothesis, we measured arterial oxygenation serially during pregnancy and again postpartum in 44 residents of Leadville, CO (elevation 3,100 m). We identified three maternal characteristics--ventilation, hemoglobin concentration, and smoking habits--that were related to the birth weight of the offspring. Mothers of smaller babies (less than 2,900 g) compared to mothers of larger babies (greater than 3,500 g) were characterized by hypoventilation, no change or a decrease in ventilation and arterial O2 saturation from early to late gestation, and a falling hemoglobin concentration that combined to lower arterial O2 content in the 3rd trimester. Maternal smoking at 3,100 m was associated with a two to threefold greater reduction in infant birth weight (-546 g) than reported from sea level. Thus, maternal arterial oxygenation during pregnancy may be important for predicting fetal growth retardation and the process of adaptation to high altitude.