High-altitude ancestry protects against IUGR and reductions in birth weight associated with high altitude and preeclampsia

Abstract

Background. Observations consistently demonstrate diminished birth weight [BW] with ascending altitude; however population comparisons reveal the extent of BW reduction depends, in part, upon high-altitude ancestry. Objective(s): To examine the influence of variable HA ancestry [Andean, European and Mestizo (admixed)] on BW, IUGR and hypertensive complications across a range of altitudes. Methods: Maternal and infant characteristics were collected from medical records of 3538 consecutive deliveries to women having 2 prenatal visits at public or private hospitals in Santa Cruz [300m, LA], Cochabamba [2500m, MA] and La Paz or Orurro [3600- 3800m, HA], Bolivia. Population ancestry was determined using parental surnames. IUGR was defined as birth weights 10th percentile for gestational age and sex using sea-level criteria. Hypertension during pregnancy was defined as two or more BP readings at least six hours apart 140/90 mmHg, or a 30/15 mmHg rise above values recorded at the first prenatal visit in a woman whose BP was 140/90 mmHg before week 20 or postpartum. Severe preeclampsia [PE] was defined BP 160/110 mmHg in late pregnancy and all other cases of PE, gestational hypertension [GH] or PE/GH were considered mild. Results: BW declined with ascending altitude [HA: 3365 18; MA: 3306 16 and LA: 3101 12; p 0.0001], however gestational age was equivalent [p NS]. BW diminished 70g, 56g and 39g per 1000m increase in elevation for Europeans, Mestizoes and Andeans, respectively. IUGR prevalence increased with altitude among Mestizo and European babies; Andeans were unaffected. Likewise, at HA, Andean BW was unaffected by mild or severe PE, whereas severe PE diminished Mestizo and European birth weight [ 346g, 1608g, respectively]; mild PE tended to increase European BW at HA [ 301.4g]. Conclusions: High-altitude ancestry protects infants from IUGR and reductions in birth weight associated with high-altitude and hypertensive complications during pregnancy.