Mothers' Ancestry Influences Weight of Babies Born at High Altitudes

After Spanish colonialists moved into South America centuries ago, almost 60 years elapsed before the European women were able to give birth successfully at the high altitudes of the Andes. But indigenous Andean women had no problems with their babies. Now some researchers from Colorado are finding out why that may have been the case.

Anthropologist Colleen Julian, who works at the Altitude Research Center at the University of Colorado, says research has shown that babies born at high altitudes tend to be smaller than those born at sea level.

"But some populations are protected from that effect," Julian says. "So, for example, women who have lived at high altitudes for extended periods of time as a population... the babies who are born to those women tend to be protected to the effects of altitudes."

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

Julian went to Bolivia to study women from indigenous Andean tribes whose ancestors have been living at high altitudes for millennia. She compared them 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. She and her colleagues interviewed women who were about 20 weeks pregnant or less and asked them extensively about their ancestry. They followed the women until delivery.

"We monitored fetal growth with ultrasound at 20 weeks of pregnancy and 36 weeks of pregnancy," Julian explains. "We looked at the amount of blood and oxygen that was getting to the baby by ultrasound at the same time points during pregnancy."

Julian and her colleagues found that in the Andean women, blood vessels supplying the uterus and placenta actually expanded to bring more blood to the fetuses. This didn't happen in the European women, even if they had been born at high altitude and had lived there all their lives.

Julian theorizes that over the millennia, indigenous people may have evolved some physiological advantages to ensure survival in the thin air of high altitude.

"It's kind of an evolutionary question, and it's a very sensitive time point at the life cycle to look at the evolutionary processes," she says. "Not only is the infant's reproductive fitness affected - their ability to pass on their genes to their prospective children - but also that of the mother and of the father, potentially."

Julian says these results point to therapeutic interventions for non-native women who get pregnant at high altitude. Perhaps, she suggests, it would be best if these women return to sea level for the duration of their pregnancies.

She says she'd also like to look further at how women's bodies have adapted to changes in altitude.

Her study is published in the Journal of Physiology-Regulatory, Integrative and Comparative Physiology.