Oxygen transport in Tibetan women during pregnancy at 3,658 m

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Abstract
High‐altitude reduces infant birth weight as a result of intrauterine growth restriction (IUGR) and is associated with increased neonatal mortality. We hypothesized that babies born to Tibetan compared to Han (Chinese) high‐altitude residents were protected from IUGR as the result of increased maternal O2 transport due, in turn, to increased uterine artery (UA) blood flow. We studied 68 nonpregnant or pregnant Tibetan or Han residents of Lhasa, Tibet Autonomous Region, China (3,658 m). The pregnant women had higher hypoxic ventilatory responses (HVR A) and resting ventilations (VE) than their nonpregnant counterparts (Tib HVR = 134 ± 16 (SEM) vs. 30 ± 8, Han HVR = 134 ± 16 vs. 66 ± 18 A units; Tib VE = 11.8 ± 0.3 vs. 10.1 ± 0.5, Han VE = 10.7 ± 0.5 vs. 9.4 ± 0.5 l BTPS/min; all P < 0.05). Pregnancy did not change hemoglobin concentration in the Han but lowered values more than 2 g/dl in the Tibetans, serving to reduce arterial O2 content below Han values (15.4 ± 0.3 vs. 17.4 ± 0.5 ml O2/100 ml whole blood, P < 0.05). Compared with the Han, the pregnant Tibetans had higher UA blood flow velocity (58.5 ± 2.9 vs. 49.1 ± 3.2, P < 0.05) and distributed a higher portion of common iliac (CI) blood flow to the UA (4.8 ± 0.4 vs. 3.3 ± 0.3, P < 0.05). Birth weights averaged 635 g greater in the Tibetan than Han high‐altitude residents (3,280 ± 78 vs. 2,645 ± 96 g, P < 0.01), or 694 g more when adjusted for maternal age, parity, height, and near‐term body weight. Heavier birth weight babies were born to women with higher VE (r = 0.62, P < 0.01) and greater distribution of CI blood flow to the UA (r = 0.42, P < 0.05). We conclude that increased UA blood flow, and not higher arterial O2 content, permits Tibetan women to increase uteroplacental O2 delivery and protect their infants from altitude‐associated IUGR. Am J Phys Anthropol 114:42–53, 2001.

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