Children who were born prematurely tend to have emotional and behavioral problems that are likely to still be present when they enter school, and to persist for at least a year, researchers say.

Past research has shown that preterm children have an increased risk of attention problems, hyperactivity, anxiety or depression and social problems, the authors write in Pediatrics.

"We found that preterm children have higher rates of persistent and changing emotional and behavioral problems at school entry - between ages 4 and 5 - than do full-term children, and that their problems are more persistent," said lead author Jorijn Hornman of the University of Groningen in The Netherlands. "The latter is really new, we did not have evidence on this."

The researchers used data from a long-term Dutch study of children born in 2002 and 2003. A full-term pregnancy lasts 39 to 41 weeks, and the analysis included 401 kids born very early, between 25 and 31 weeks of pregnancy, as well as 653 kids born moderately preterm, between 32 and 35 weeks, and 389 kids born at full term.

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At ages 4 and 5 years, the children were assessed for emotional and behavioral problems.

Overall, more than 7 percent of preterm children had emotional or behavioral problems at both time points, compared with less than 4 percent of full-term children. There was a similar difference between groups for problems that appeared at age 4 and had resolved by age 5.

Early pre-term children had the highest rates of persistent emotional and behavioral problems, at just over 8 percent.

"Persistence of a problem usually indicates a chronic problem and these have been shown in other research to have higher persistence into adolescence," said Dieter Wolke, professor of Developmental Psychology and Individual Differences at Warwick Medical School U.K., who was not part of the new study.

Issues that were not present at age 4 but emerged at age 5 were less common, affecting 4 percent of preterm kids and 2 percent of full-term kids.

The earlier a child was born, the more likely they were to have emotional or behavioral problems.

"The brain develops very fast in the last weeks of pregnancy, especially the reorganization and differentiation of newly formed neural networks," Hornman told Reuters Health by email. "Preterm delivery may disrupt this," and could increase the risk of long-term emotional and behavioral problems.

These problems could have a large impact on school performance and interaction with other children, she said.

"We do not yet have evidence on persistence into adulthood," Hornman said.

Early detection, parenting support and timely referral to specialized care helps give preterm children the best start at school, she said.

"These findings may help to determine before school entry which preterm children are likely to have increased risks of emotional and behavioral problems when attending school," Hornman said. "The good news is that 90 percent of the moderately preterm children and 80 percent of the early preterm children are consistently without emotional and behavioral problems between age 4 and 5."

"Parents of very preterm kids should be aware that there may be an increased risk (despite most developing within normal limits) and indicate to teachers and mental health professionals that their child was born very preterm to assist them with the right interventions," Wolke said.