Greater uterine artery blood flow during pregnancy in multigenerational (Andean) than shorter-term (European) high-altitude residents

Multigenerational (Andean) compared with shorter-term (European) high-altitude residents exhibit less hypoxia-associated reductions in birth weight. Because differences in arterial O₂ content are not responsible, we asked whether greater pregnancy-associated increases in uterine artery (UA) blood flow and O₂ delivery were involved. Serial studies were conducted in 42 Andean and 26 European residents of La Paz, Bolivia (3600 m) at weeks 20, 30, 36 of pregnancy and 4 mo postpartum using Doppler ultrasound. There were no differences postpartum but Andean vs. European women had greater UA diameter (0.65 ± 0.01 vs. 0.56 ± 0.01 cm), cross-sectional area (33.1 ± 0.97 vs. 24.7 ± 1.18 mm²), and blood flow at week 36 (743 ± 87 vs. 474 ± 36 ml/min) (all P < 0.05) and thus 1.6-fold greater uteroplacental O₂ delivery near term (126.82 ± 18.47 vs. 80.33 ± 8.69 ml O₂·ml blood^-1·min^-1, P < 0.05). Andeans had greater common iliac (CI) flow and lower external iliac relative to CI flow (0.52 ± 0.11 vs. 0.95 ± 0.14, P < 0.05) than Europeans at week 36. After adjusting for gestational age, maternal height, and parity, Andean babies weighed 209 g more than the Europeans. Greater UA cross-sectional area at week 30 related positively to birth weight in Andeans (r = +0.39) but negatively in Europeans (r = -0.37) (both P < 0.01). We concluded that a greater pregnancy-associated increase in UA diameter raised UA blood flow and uteroplacental O₂ delivery in the Andeans and contributed to their ability to maintain normal fetal growth under conditions of high-altitude hypoxia. These data implicate the involvement of genetic factors in protecting multigenerational populations from hypoxia-associated reductions in fetal growth, but future studies are required for confirmation and identification of the specific genes involved.