Lowland origin women raised at high altitude are not protected against lower uteroplacental O2 delivery during pregnancy or reduced birth weight

Abstract

Objective. Maternal physiologic responses to pregnancy promoting fetal oxygen and nutrient delivery are important determinants of reproductive success. Incomplete physiologic compensation for reduced oxygen availability at high altitude ( 2,500 m) compromises fetal growth. Populations of highland (e.g., Andeans, Tibetans) compared with lowland origin groups (e.g., Europeans, Han Chinese) are protected from this altitude-associated decrease in birth weight; here we sought to determine whether maternal development at high altitude—rather than highland ancestry—contributed to the protection of birth weight and uterine artery (UA) blood flow during pregnancy. Methods. In women of lowland ancestry who were either raised at high altitude in La Paz, Bolivia (3,600–4,100 m) (‘‘lifelong,’’ n 5 18) or who had migrated there as adults (‘‘newcomers,’’ n 5 40) we compared maternal O2 transport during pregnancy and their infant’s birth weight. Results. Pregnancy raised maternal ventilation and arterial O2 saturation equally, with the result that arterial O2 content was similarly maintained at nonpregnant levels despite a fall in hemoglobin. UA blood flow and uteroplacental O2 delivery were lower in lifelong than newcomer residents (main effect). Birth weight was similar in lifelong residents versus newcomers (2,948 6 93 vs. 3,090 6 70 gm), with both having values below those of a subset of eight high-altitude residents who descended to deliver at low altitude (3,418 6 133 gm, P < 0.05). Conclusion. Lifelong compared with newcomer high-altitude residents have lower uteroplacental O2 delivery and similar infant birth weights, suggesting that developmental factors are likely not responsible for the protective effect of highland ancestry.