Abstract

Objective: The chronic hypoxia of high-altitude (? 2500m) residence decreases birth weight in all populations studied to date. However, multigenerational high-altitude populations appear protected relative to newcomer groups. Our aim was to determine whether such protection exists independently of other factors known to influence fetal growth and whether admixed populations (i.e. persons having both high- and low- altitude ancestry) show an intermediate level of protection.

Design: 3551 medical records from consecutive deliveries to Andean, European or Mestizo (i.e. admixed) women at low, intermediate or high altitudes in Bolivia were evaluated for maternal characteristics influencing fetal growth as measured by birth weight and the frequency of small-for-gestational-age births (SGA or <10th percentile birth weight for gestational age and sex). Two-way ANOVA and chi-square were used to compare maternal and infant characteristics. The effects of ancestry or altitude on SGA and birth weight were assessed using logistic or linear regression models, respectively.

Results: Altitude decreased birth weight and increased SGA in all ancestry groups. Andeans weighed more and were less often SGA than Mestizos or Europeans at high altitude (SGA: 13%, 16% and 33% respectively, p<0.01). After accounting for the influences of maternal hypertensive complications of pregnancy, parity, body weight, and number of prenatal visits, European relative to Andean ancestry increased the frequency of SGA at high altitude nearly 5-fold.

Conclusions: Andean relative to European ancestry protects against altitude-associated reductions in fetal growth. The intermediate protection seen in the admixed (Mestizo) group is consistent with the involvement of genetic or other Andean-specific protective characteristics.