To make matters worse, preemies are also more likely to develop attention deficits, hyperactivity and other emotional and behavioral problems, a new study has found.

Such a difference on a cognitive test may be trivial between two individuals in the normal range of intelligence. However, for preemies as a whole -- and especially extremely immature infants -- experts say the gulf is alarming, since their average scores are lower than full-term babies.

"There is a huge educational handicap for children born premature," says study co-author Dr. K. J. S. Anand, a pediatrician at the University of Arkansas. "Gradually, these children are making up a greater and greater proportion of the children that are going through school, which is very concerning. I really think our educational system is in for a shock because of these figures."

One study the researchers reviewed found that preemies or low-birth weight infants were 50 percent more likely than full-term babies to wind up in special education -- with the extra cost of teaching them estimated at $370 million in 1988 alone.

A report on the study appears in tomorrow's Journal of the American Medical Association.

Preemie deliveries -- defined as being less than 37 weeks' gestation -- are still relatively rare, making up about 11 percent or so of births in this country. However, the rate has been rising over the past two decades, thanks in part to the growing use of fertility drugs that promote multiple pregnancies and improvements in neonatal care that keep even the lightest, least mature babies alive.

Researchers have performed hundreds of studies looking for evidence of developmental difficulties among preemies, and especially those born extremely early and underweight.

From poorer academic performance to brain anomalies caught on imaging tests, the evidence exists.

However, many of these reports have been rife with methodological flaws, souring their results and weakening their conclusions, Anand says. Some, for example, used different cognitive tests for preemies and on-time babies. Others included children with brain bleeding that may accompany birth troubles related to prematurity. Others have had a hard time accounting for the effects of cerebral palsy, which disproportionately afflicts preemies.

In the latest work, Anand, who is also chief of critical care medicine at Arkansas Children's Hospital, and his colleagues tried to iron out these wrinkles to draw a smoother picture of the long-term effects of prematurity.

The researchers analyzed 31 of 227 previous studies of preemies that included evidence of both behavioral and mental outcomes. In all, the studies covered 1,556 preemies and 1,720 on-time babies.

The average score on cognitive tests -- an early measure of IQ -- was 10.9 points higher for the children born on time than for those born early, Anand's group found. The deficit was even greater for the more premature and the more underweight.

Premature infants were also about 2.6 times more likely than the other babies to develop attention deficit-hyperactivity disorder (ADHD) by the time they entered school. They also had a greater risk of other behavioral troubles such as profound shyness, frustration and stranger anxiety, as well as problems with aggression, delinquency and destructiveness.

Dr. Maureen Hack is a noted expert in the long-term outcomes of preemies at Cleveland's Rainbow Baby's and Children's Hospital. Hack says the latest study helps cement the evidence that these infants truly face disadvantages later in life.

"We know they have problems at school age, they do persist into adolescence, and they do have implications for adulthood," she says. Even accounting for lower scores on cognitive tests, preemies suffer developmental trouble.

"Fewer of them finish high school, especially the men, and fewer of them go to college" compared with children who were born full-term, she says.

What To Do

To learn more about prematurity, check out the American Association for Premature Infants or the University of Wisconsin.