Fetal growth is reduced at high altitude, but the decrease is less among long-resident populations. We hypothesized that greater maternal uteroplacental O 2 delivery would explain increased fetal growth in Andean natives versus European migrants to high altitude. O 2 delivery was measured with ultrasound, Doppler and haematological techniques. Participants (n = 180) were pregnant women of self-professed European or Andean ancestry living at 3600 m or 400 m in Bolivia. Ancestry was quantified using ancestry-informative single nucleotide polymorphims. The altitude-associated decrement in birth weight was 418 g in European versus 236 g in Andean women (P < 0.005). Altitude was associated with decreased uterine artery diameter, volumetric blood flow and O 2 delivery regardless of ancestry. But the hypothesis was rejected as O 2 delivery was similar between ancestry groups at their respective altitudes of residence. Instead, Andean neonates were larger and heavier per unit of O 2 delivery, regardless of altitude (P < 0.001). European admixture among Andeans was negatively correlated with birth weight at both altitudes (P < 0.01), but admixture was not related to any of the O 2 transport variables. Genetically mediated differences in maternal O 2 delivery are thus unlikely to explain the Andean advantage in fetal growth. Of the other independent variables, only placental weight and gestational age explained significant variation in birth weight. Thus greater placental efficiency in O 2 and nutrient transport, and/or greater fetal efficiency in substrate utilization may contribute to ancestry-and altitude-related differences in fetal growth. Uterine artery O 2 delivery in these pregnancies was 99 ± 3 ml min −1 , ∼5-fold greater than near-term fetal O 2 consumption. Deficits in maternal O 2 transport in third trimester normal pregnancy are unlikely to be causally associated with variation in fetal growth.

BackgroundThe most well known reproductive consequence of residence at high altitude (HA >2700 m) is reduction in fetal growth. Reduced fetoplacental oxygenation is an underlying cause of pregnancy pathologies, including intrauterine growth restriction and preeclampsia, which are more common at HA. Therefore, altitude is a natural experimental model to study the etiology of pregnancy pathophysiologies. We have shown that the proximate cause of decreased fetal growth is not reduced oxygen availability, delivery, or consumption. We therefore asked whether glucose, the primary substrate for fetal growth, might be decreased and/or whether altered fetoplacental glucose metabolism might account for reduced fetal growth at HA.MethodsDoppler and ultrasound were used to measure maternal uterine and fetal umbilical blood flows in 69 and 58 residents of 400 vs 3600 m. Arterial and venous blood samples from mother and fetus were collected at elective cesarean delivery and analyzed for glucose, lactate and insulin. Maternal delivery and fetal uptakes for oxygen and glucose were calculated.Principal FindingsThe maternal arterial – venous glucose concentration difference was greater at HA. However, umbilical venous and arterial glucose concentrations were markedly decreased, resulting in lower glucose delivery at 3600 m. Fetal glucose consumption was reduced by >28%, but strongly correlated with glucose delivery, highlighting the relevance of glucose concentration to fetal uptake. At altitude, fetal lactate levels were increased, insulin concentrations decreased, and the expression of GLUT1 glucose transporter protein in the placental basal membrane was reduced.Conclusion/SignificanceOur results support that preferential anaerobic consumption of glucose by the placenta at high altitude spares oxygen for fetal use, but limits glucose availability for fetal growth. Thus reduced fetal growth at high altitude is associated with fetal hypoglycemia, hypoinsulinemia and a trend towards lactacidemia. Our data support that placentally-mediated reduction in glucose transport is an initiating factor for reduced fetal growth under conditions of chronic hypoxemia.

Fetal growth is decreased at high altitude (> 2700 m). We hypothesized that variation in fetal O 2 delivery might account for both the altitude effect and the relative preservation of fetal growth in multigenerational natives to high altitude. Participants were 168 women of European or Andean ancestry living at 3600 m or 400 m. Ancestry was genetically confirmed. Umbilical vein blood flow was measured using ultrasound and Doppler. Cord blood samples permitted calculation of fetal O 2 delivery and consumption. Andean fetuses had greater blood flow and oxygen delivery than Europeans and weighed more at birth, regardless of altitude (+208 g, P < 0.0001). Fetal blood flow was decreased at 3600 m (P < 0.0001); the decrement was similar in both ancestry groups. Altitude-associated decrease in birth weight was greater in Europeans (−417 g) than Andeans (−228 g, P < 0.005). Birth weight at 3600 m was > 200 g lower for Europeans at any given level of blood flow or O 2 delivery. Fetal haemoglobin concentration was increased, P CO 2 decreased, and the fetal P O 2 /S O 2 curve was left-shifted at 3600 m. Fetuses receiving less O 2 extracted more (r 2 = 0.35, P < 0.0001). These adaptations resulted in similar fetal O 2 delivery and consumption across all four groups. Increased umbilical venous O 2 delivery correlated with increased fetal O 2 consumption per kg weight (r 2 = 0.50, P < 0.0001). Blood flow (r 2 = 0.16, P < 0.001) and O 2 delivery (r 2 = 0.17, P < 0.001) correlated with birth weight at 3600 m, but not at 400 m (r 2 = 0.04, and 0.03, respectively). We concluded that the most pronounced difference at high altitude is reduced fetal blood flow, but fetal haematological adaptation and fetal capacity to increase O 2 extraction indicates that deficit in fetal oxygen delivery is unlikely to be causally associated with the altitude-and ancestry-related differences in fetal growth.

Trypanosoma cruzi infection was studied in 1,298 sera samples of blood banks from 7 capital departments of Bolivia, using the immunofluorescence test (IFI) and Enzyme Linked Immunosorbent Assay (ELISA). The percentages of positivity in these 7 departments have an average of 28% and are distributed as follows: Sta. Cruz 51%, Tarija 45%, Cochabamba 28%, Sucre 39%, La Paz 4.9%, Oruro 6% and Potosi 24%. The prevalence is related with the altitude levels of the different departments. However in Potosi (3,945 m) we found a 24% of prevalence, probably due to the proximity of endemic valleys to the city. The authors suggest a strict control in blood donors since there exists a great risk of infection.