Babies born at very low birth weights often experience learning difficulties and behavioral problems as young children, but these problems do not necessarily translate into lower education levels and salaries as adults, according to a new study.

These children can adapt, and for the most part, their education level and earnings are on par with those who are born at a normal weight, the researchers said.

"It seems that there is a longer period of catch-up ... and the earlier reports, which are not very favorable, do not mean that children will not improve over time," said Dr. Saroj Saigal, of McMaster University in Ontario, Canada. "By adulthood, the majority of children are doing much better than we would ever have predicted."

However, men born at very low birth weights appear to experience more detrimental effects in adulthood than women, completing slightly fewer years of education , and earning less on average than adults born at normal weights, the researchers said.

The researchers noted their study took place in Canada, so the children may have received more social support than those living in other countries. As a result, the "catch-up" might not be as great for children in countries lacking such a safety net, such as the United States, they said.

Tiny babies

About one-fourth of children born at extremely low birth weights , weighing less than 2.2 pounds, have impairments in their nervous systems, such as mental retardation. The brains of babies born that early are more prone to injuries from complications, such as hemorrhaging or lack of oxygen, Saigal said. About half of extremely low birth weight children require special education or have repeated a grade in school by age 9.

Today, about 80 percent of babies born at this weight survive, she said.

While many studies have looked at the effects of very low birth weight on children's success in their early school years, few have examined adulthood. This is mainly because, before about 1970, few children survived if they weighed about 2 pounds.

"The survivors are only [now] reaching the age where they're entering the labor market in significant numbers," said study researcher John Goddeeris, a professor of economics at Michigan State University.

The researchers looked at the years of school completed and the amount of money earned by 149 young adults who were born at extremely low birth weights. They compared these people to a group of 143 adults similar in age, gender and socioeconomic status.

People born at low birth weights were just as likely as normal birth weight adults to complete high school when the researchers took into account nervous system impairments. (More than one-fourth of the participants born at low birth weights had such an impairment, while just 2 percent of the normal birth weight group did. The researchers wanted to see if, after they removed the effects of these impairments, being born at a low birth weight had an impact.)

However, men completed 1.1 fewer years of education on average than those in the normal-weight group. Men also saw a 20 percent reduction in their earnings compared with the normal weight group, after the researchers accounted for nervous system impairment and low IQ. Low birth weight women were no different from normal weight women in terms of their education and earnings.

Productive adults

While the study was fairly small, the findings agree with those of larger studies recently completed in Europe, the researchers said.

"The picture that seems to emerge is that you can see some effects of being extremely low birth weight, or extremely premature, but they're not really that huge," Goddeeris said. "Most of them do become productive citizens, and they make this transition to adulthood."

However, Goddeeris noted a small group of children will experience severe impairments that prevent them from functioning as normal adults. "I'm not saying that there isn't a group who are very much affected, but that's a relatively small fraction of the survivors," he said.

The study was published in the November Issue of the journal Pediatrics.