Babies Born at Altitude

Researchers have found that babies born at high altitudes (>8,000 feet) are about three times as likely to be born small for their age as babies born at low altitudes. In Colorado birth weight declines an average of just over 3.5 ounces per 3,300 feet of elevation.

These babies aren't smaller because they're born earlier. The lower pressure at high altitude means less oxygen is available in the air, which results in the baby receiving less oxygen and fewer nutrients. This leads to slower growth rate, especially in the third trimester, when a baby's growth rate and need for oxygen and nutrients are the highest.

Altitude Natives Have Adapted

ARC studies women from indigenous Andean tribes in Bolivia whose ancestors have been living at high altitude for millennia. They are compared to European women who were in the area only temporarily or whose families may have migrated to the high Andes only a generation or two ago.  Our study showed that in the Andean women, blood vessels supplying the uterus and placenta actually expanded to bring more blood to the fetus. Contrary to the Andeans, the European women didn't show this expansion, even if they had been born at high altitude and had lived there all their lives.  This could very well indicate that, over many years, indigenous people have evolved some physiological advantages that increase their chances of survival at high altitude.

Around the world, about 150 million people live at high altitudes in places like the Himalaya, the Ethiopian highlands and the Andes Mountains of South America. 

Scientific abstract