To study the effects of altitude on infant neurodevelopment in the first 2 years of life.

Data from a unique study of normal infant neurodevelopment in 5 South American countries were used. The sample included 2116 infants 3-24 months of age who were evaluated for neurodevelopmental problems by study physicians during their routine well-child visits at 31 pediatric practices. We used regression models with country fixed-effects that compare the neurodevelopment of children born at different altitudes within the same country to avoid confounding. The regressions adjust for several socioeconomic and demographic factors. We also evaluated altitude effects stratifying by sex, age, and household wealth. Infant neurodevelopment was evaluated by physicians by using the Bayley Infant Neurodevelopmental Screener. The primary outcome is an indicator for whether the infant is at high risk for neurodevelopmental problems based on the Bayley Infant Neurodevelopmental Screener norms.

Altitude significantly increases the probability of being at high risk for neurodevelopmental problems (100-meter increase in altitude: OR 1.02; 95% CI 1.001-1.037; high altitude greater than 2600 meters vs low altitude less than 800 meters: OR 2.01; 95% CI 1.36-2.973). The effects are larger for females and for second than first year of life. The largest effect is for females 12-24 months of age (high vs low altitude: OR 4.147; 95% CI 1.466-12.013). There are no significant differences in altitude effects by household wealth.

Altitude may significantly increase the risk of neurodevelopmental problems during the first 2 years of life, especially for females during their second year of life.