NEW YORK - Children who were born prematurely and at a very low weight may have an increased risk of certain behavior problems and symptoms of depression and anxiety, research suggests.

As the survival rates of very preterm newborns have improved in recent years, studies have uncovered some of the potential long-term challenges these infants will face -- including lower IQ and higher rates of behavioral problems compared with their peers born at term.

In the new study, researchers found that among 104 7- to 16-year-olds they assessed, the 49 who were born very prematurely had higher rates of hyperactivity and attention problems, as well as symptoms of depression and anxiety.

The higher risk was not explained by lower IQ scores, however. Nor was families' socioeconomic status an important factor in children's odds of behavioral or emotional issues.

Instead, birth weight itself was the strongest factor, the researchers report in the journal Pediatrics.

The finding "suggests that in children born prematurely, behavioral issues might be more biologically based and not easily compensated for by improvements in the environment," explained lead researcher Dr. Amy L. Conrad, of the University of Iowa College of Medicine in Iowa City.

"It does not mean that environment can't help," she told Reuters Health in an email, "just that it might not have as strong of an impact as for children born at term and of average birth weight."

In addition, while the study found that parents of premature children reported more behavioral and emotional symptoms than other parents did, most kids did not have significant problems.

According to Conrad, 18 percent of preterm children had hyperactivity/inattention problems that were in the "clinical range" -- or significant enough to warrant therapy -- while 14 percent had depression or anxiety symptoms in that range.

For the study, Conrad's team had 104 children and teenagers take standard intelligence tests, while their parents and teachers completed a standard questionnaire on behavioral issues. Forty-nine of the kids had been born significantly preterm -- between the 24th and 33rd week of pregnancy. A normal pregnancy lasts 40 weeks.

Their birth weights ranged from "extremely low" -- less than 2.2 pounds -- to "very low," or between 2.2 and 3.3 pounds.

In general, parents of preterm children reported more behavioral issues than parents of children born full-term, with the highest rates among children with extremely low birth weights. The link between birth weight and behavior did not fade after the researchers factored in children's age, gender, IQ and socioeconomic status.

It's possible that very low birth weight affected some children's brain development in a way that made them more vulnerable to behavioral problems. Conrad said that the aim of her team's future research is to help answer that question.

For now, she said, parents of premature children should be aware of the higher risk of behavioral issues and be on the lookout for potential signs of problems.

"If parents notice issues of inattention, hyperactivity, depression or anxiety that are not age-appropriate and interfere with everyday life," she said, "they would want to consult their doctor or seek referral to a local psychologist."