By E.J. Mundell

NEW YORK, Mar 28 (Reuters Health) -- Oxygen deprivation in the womb may cause babies born at high altitudes to be smaller and less healthy at birth than babies born at lower elevations, researchers report.

"There was a threshold at about 2,000 meters (6,600 feet)," noted study lead author Dr. Jacopo Mortola, of McGill University in Montreal, Canada. "As soon as you move above that then there is a progressive drop (in birth weight) of about 60 grams (about 2 ounces) per every 500 meters altitude," he said. His team's findings are published in the March issue of The Journal of Pediatrics.

The researchers examined data on births to women living at various altitudes in Peru, which rises from sea level at the Pacific coast to more than 6,000 meters (20,000 feet) in the high Andes.

The team found steep reductions in birth weight at high elevations. The reason: hypoxia, which is a decline in the amount of oxygen available to tissues. In the cases under study, fetal hypoxia was linked to the 'thinner' air mothers breathe at high altitudes.

Experts believe that hypoxia slows fetal growth by lowering metabolic rate. "Basically, the fetus is trying to save energy, to use less oxygen, and shuts (or slows) down a variety of functions" -- including cell growth, Mortola said in an interview with Reuters Health. Hypoxia-related slowdowns in growth often end in the full-term delivery of smaller infants.

Developmental and health problems may continue throughout the life span if children born with hypoxia remain at low-oxygen altitudes. "Many of the characteristics they have at birth are not only not going to be reversed but may actually get worse," Mortola explained. These include blood disorders, heart and lung dysfunction, and, ultimately, a tendency toward shorter life spans. The long-term neurological effects of chronic hypoxia remain unclear.

According to Mortola, Peruvian families have known for generations that high-altitude pregnancies can have a negative impact on children's health. In fact, many Peruvian women move to lower altitudes to wait out their pregnancies, with some remaining at sea level for up to a year after delivery. Mortola recommends that "if the mother has the means -- the monetary support, the family support -- that would provide her with life at sea level during gestation, it would be a tremendous improvement."

Unfortunately, humans appear to be slow in adapting to life at the top of the world. Even though people first settled in the high Andes centuries ago, "in evolutionary terms this is still a very short period of time," Mortola explained. He noted that "if you compare our responses to those of yaks and llamas, animals which are really well-adapted to high altitudes, you can see the difference."

SOURCE: The Journal of Pediatrics 2000;136:324-329.

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