High-altitude pregnancies typically produce lower birth weight infants, even among women whose families have lived in high altitude for centuries. However, the babies of these women weigh more at birth compared to women whose ancestors have not lived at high altitude. European infants are three times more likely to be born small for their gestational age compared to Andean babies.
The same is true when comparing groups of women in other areas of the world, according to Dr. Julian, the study's lead author. Native Tibetan women's babies weigh more than the babies of Han women, a Chinese population that recently moved to the high altitude of Tibet. It is not clear what accounts for these differences, but they may occur because of differences in:
Most likely, it is both the placenta and the uterine artery that accounts for these differences between Europeans and Andeans, Dr. Julian said.
More than 12,000 feet
The study took place in Bolivia and included two groups: pregnant women living at sea level and pregnant women living in the Andes Mountains (12,000 to14,000 feet). Each group included women of Andean and European ancestry. The researchers determined Andean ancestry through a combination of three methods: genetic testing, interviews and surnames.
The research focused on the uterine artery, which dilates to increase blood flow to the fetus during pregnancy. The low-oxygen environment at altitude affects the uterine artery, reducing blood flow and oxygen delivery to the infant. Reduced blood flow and oxygen slows fetal metabolism and results in slower growth.
The study predicted that this reduction in blood flow at altitude would be much les
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American Physiological Society