South American babies and toddlers living at high altitude were more likely to score poorly on early tests of brain development, in a new study.

Of all kids age three months to two years, one in five was at high risk of developmental delays, according to tests done at their pediatricians' offices. That rose to between one in three and one in four for those who lived above 2,600 meters, or 8,530 feet.

Because there is less oxygen at higher elevations, researchers said blood flow in the uterus may also be decreased at altitude - which could impact the brain of a developing fetus.

"The findings emphasize the need for health care providers and policy-makers to recognize that altitude may increase developmental risks not just for physical growth, as has been reported, but for neurologic and cognitive development," wrote George Wehby from the University of Iowa in Iowa City, who conducted the research.

His study involved over 2,000 young kids evaluated at offices in Argentina, Brazil, Bolivia, Chile and Ecuador in 2005 and 2006.

The babies and toddlers were all given a series of problem-solving and motor tasks to complete, which their doctors used to measure which ones might be at risk for delayed development.

Wehby found that on average, for every 100-meter (328-feet) increase in elevation, kids were 2 percent more likely to be judged at high risk of future developmental problems.

Compared to kids living below 800 meters (2,625 feet), those above 8,530 feet were twice as likely to be at high risk, according to their pediatricians' evaluations.

The study, funded by the National Institutes of Health, is published in The Journal of Pediatrics.

All of the babies in Bolivia lived above the 8,530-foot cut-off, and all the kids in Argentina, Brazil and Chile lived below it. Ecuador was the only country in the study that included kids from both high- and low-altitude regions.

Of the largest cities in the United States, Albuquerque has a high point of 6,120 feet and Denver of 5,470 feet. Many Western states - including California, Colorado, Nevada and Utah - have regions above 10,000 feet.

However, it's hard to know whether the results apply to other communities at high elevation, according to Alexis Handal, an epidemiologist from the University of New Mexico in Albuquerque, who does her research in Ecuador.

"We're starting to realize there's such a complicated social context within which these populations live that it's very hard to look at one area and try to generalize to other areas," Handal, who wasn't involved in the new study, told Reuters Health.

For example, she said, parents' work hours, whether families have access to nutritious food and what environmental toxins communities might be exposed to can all interact with factors like altitude to influence maternal and child health.

"Perhaps what we also have to focus on is... how can we also develop programs that promote infant development, that help families?" she added.

Wehby said in the study that babies born at higher elevations may be helped by earlier health screening to make sure they're developing normally.

But he also pointed to the need for more research on why altitude may affect development - and whether similar patterns apply to kids in other high-altitude regions.