by Karla Gale

NEW YORK (Reuters Health) – Physical, cognitive, and social impairments impact the lives of many adults who were born prematurely, according to a national cohort study in Norway published in the New England Journal of Medicine for July 17.

"What most surprised us was the consistency of a dose-response relationship between gestational age and nearly all of the outcomes studied," lead author Dr. Dag Moster told Reuters Health. "On the other hand, we were reassured by our findings that the majority of preterm children without medical disabilities actually seemed to function very well as adults."

Dr. Moster and colleagues at the University of Bergen linked national registries to identify children of different gestational age categories born between 1967 and 1983 and who survived until 2003. The cohort included close to 870,000 live births of at least 23 weeks’ gestational age without congenital anomalies.

Within the most preterm category, the risk of cerebral palsy increased over time, reflecting higher rates of survival among these vulnerable infants. Overall, 6% of those born at 28-30 weeks and 9% of those born at 23-27 weeks had cerebral palsy, for relative risks compared with term births of 46 and 79, respectively (p < 0.001).

"An ongoing study of children born in Norway in 1999-2000 demonstrates a survival rate to 5 years of age of 80% among 23-27 weekers, a notable increase compared to the 20% survival rate in our study. Sadly, the rates of cerebral palsy in these two studies are very much the same," Dr. Moster commented.

Results also showed significant trends for mental retardation; disorders of psychological development, behavior and emotion; and severe vision or hearing impairment or epilepsy, with relative risks ranging from 10 to 20 for the earliest births.

When they excluded persons with medical disabilities from their analyses, there were small but statistically significant associations between gestational age and educational achievement, job-related income, finding a life partner, and of having children.

In contrast, there was no significant difference in unemployment rates, drug arrests, violent behavior, or other criminal activity.

"There was an increased risk of disabilities even among moderate preterm children," whose numbers far exceed those of the most premature children, Dr. Moster pointed out. "Most research so far has focused on the most immature children, but the current study demonstrates that improving outcome for moderate preterm children would have an even greater impact on the number of disabled children."

"Studies are needed to identify modifiable factors that predict adult outcomes among children born prematurely in order to improve preventive and therapeutic strategies," the investigators conclude.

N Engl J Med 2008;359:262-273.

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