The findings of the study were reported in the Archives of Diseases in Childhood and involved 30,000 Danish children.  It was an extension of previous studies that have demonstrated the presence of ADHD in children whose birth was very premature – at less than 28 weeks gestation.

  This was the first study, however, that examined children born at 34-36 weeks.

Researchers used data from Danish national registers to compare the risk of ADHD or the related hyperkinetic disorder and preterm birth in 834 children with the conditions and 20,100 controls, notes an article published by the BBC. 

The study goes on to point out that babies born at term but weighing between 3lb 3oz and 5lb 5oz (1.5kg to 2.5kg) at birth were 90% more likely to develop hyperactivity disorder and ADHD than those of normal weight.  A 50% increased risk in developing the disorder was associated with a birth weight of between 5 lb, 6 oz. to 6 lb, 6 oz. 

The report also showed that about 90% of those with Attention Deficit Hyperactivity Disorder are boys. 

Professor James Walker, consultant obstetrician at St James Hospital in Leeds, England said the study showed the risk of ADHD was not just confined to very preterm babies but that the earlier babies were born the more likely they were to have various developmental problems.

"It's probably to do with nutrition and I suspect some of the problems may have been overcome as nutrition for neonates has got a lot better," he said.