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Low birth weight infants may have cognitive and physical problems when they reach adolescence

October 03, 2006

Sixteen-year-olds who weighed less than 2,000 grams (about 4.5 pounds) at birth and are not disabled are still more likely than the average teenager to have physical and mental difficulties, according to a report in the October issue of Archives of Pediatrics & Adolescent Medicine, one of the JAMA/Archives journals.

Low birth weight is known to increase the risk for major disabilities such as cerebral palsy and mental retardation, but researchers now suspect that low birth weight may also contribute to minor difficulties in motor skills and in thinking, learning and memory (cognitive abilities). These problems may last into adolescence, according to background information in the article.

Agnes H. Whitaker, M.D., Columbia University and New York State Psychiatric Institute, New York, and colleagues studied 474 non-disabled adolescents who were born at or admitted to one of three New Jersey hospitals between 1984 and 1987 and weighed less than 2,000 grams at birth. The participants, who had an average age of 16 at the time of assessment for this study, underwent intelligence and motor tests in their homes.

Compared with the standardization sample, or the large group of teens used to provide a reference point for the assessments, the adolescents with low birth weight had more motor problems. Their IQ scores were within the normal range, but on average were significantly lower than the average for their age group. Those who were male, who had injuries to the white matter (nerve tissue) of the brain on neonatal ultrasound and who spent more days on a ventilator as an infant were more likely to have motor difficulties. Social disadvantages, a lower fetal growth ratio (calculated by dividing birth weight by the median weight for the infant's age) and white matter injury also predicted lower IQ scores.

"The finding that, independent of social risk, specific prenatal, perinatal and neonatal biological risk factors are associated with cognitive and motor outcomes as late as adolescence runs counter to the view that, absent severe disability, early biological risk factors are of little importance in later life," the authors conclude. "The prevention of white matter injury and the need for mechanical ventilation may be key to improving motor outcomes, whereas the prevention of intrauterine growth retardation (or perhaps impaired head growth) and white matter injury may be key to improving cognitive outcomes. Taken together, these findings suggest that enhanced maternal-fetal and neonatal care have the potential to substantially improve cognitive and motor outcomes for non-disabled low birth weight adolescents."

JAMA and Archives Journals