Babies born to native high-altitude mothers have decreased risk of low birth weight

Pregnant women who are indigenous to the Andes Mountains deliver more blood and oxygen to their fetuses at high altitude than do women of European descent. The study helps explain why babies of Andean descent born at high altitude weigh more than European babies born at altitude.

The research, published in The American Journal of Physiology-Regulatory, Integrative and Comparative Physiology found that at high altitude:

* the uterine artery of Andean women delivered more blood and oxygen to the fetus compared to women of European descent
* the babies of Andean women weighed an average of nine ounces more at birth
* the greater the mother’s Andean heritage, the greater the uterine artery blood flow, the greater the oxygen delivery to the fetus and the greater the baby’s birth weight

These differences between the Andean and European women and their babies did not exist at low altitude.

The question of why babies born at high altitude are smaller is not an academic one. Low birthweight is associated with higher rates of illness and mortality. By understanding this physiology, researchers hope to find out how to protect from reductions in fetal growth even in low-oxygen environments.

The study, “Augmented uterine artery blood flow and oxygen delivery protect Andeans from altitude-associated reductions in fetal growth.” was done by Colleen Glyde Julian, Megan J. Wilson, Henry Yamashiro and Lorna G. Moore of the University of Colorado; Wilma Tellez, Armando Rodriguez and Enrique Vargas of Universidad Mayor de San Andrés, La Paz, Bolivia; Abigail Bigham and Mark Shriver of Pennsylvania State University; and Miriam Lopez of Clínica del Sur, La Paz, Bolivia. Dr. Yamashiro is also affiliated with Clinica Siraní, Santa Cruz de la Sierra, Bolivia and Dr. Moore is also affiliated with Wake Forest University, Winston-Salem, North Carolina.

Birth weight differences

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:

* how much oxygen the mother is able to deliver through the uterine artery
* how much nutrition and/or oxygen the mother is able to deliver through the placenta* a combination of both uterine artery and placental factors