Premature babies face higher risk of hyperactivity

Premature babies face higher risk of hyperactivity

* 18:36 05 June 2006
* NewScientist.com news service
* Roxanne Khamsi

Babies born prematurely face a significantly greater risk of developing attention deficit hyperactivity disorder (ADHD), Danish researchers report.

The results should encourage women to take precautions against premature birth, including refraining from smoking, says study author Karen Linnet of the Aarhus University Hospital in Denmark.

Her team mined information from a national database that included 834 children born between 1980 and 1994 who had been diagnosed with ADHD, which is characterised by extreme inattentiveness and restlessness. They also reviewed data from more than 20,000 children without the disorder.

After controlling for the socioeconomic status of the parents, the analysis revealed that compared with babies born at full term, those born prematurely following 34 to 36 weeks' gestation had a 70% greater risk of developing ADHD. And babies born before 34 weeks were nearly three times as likely to develop the disorder as those born at term.
Low birthweight

A previous study had found that babies born before 28 weeks of gestation faced a higher risk of developing ADHD (Acta Paediatrica, vol 88, p 557). But the new study is important because the majority of preterm deliveries are after 28 weeks of gestation, says Linnet.

Her study also found that babies with a low birthweight faced an increased risk of developing ADHD. Those born at full term but weighing 1.5 to 2.5 kilograms had a 90% greater chance of later being diagnosed with ADHD than babies born weighing more than 3 kilograms.

Premature babies are known to have a greater risk of oxygen deprivation and low blood pressure while in the womb. In animal tests these conditions led to more receptors for the neurotransmitter dopamine in certain parts of the brain, explains Linnet.

Since humans with ADHD are thought to have more dopamine receptors in their brains, this might explain the link between preterm birth and the disorder, she suggests.

Journal reference: Archives of Disease in Childhood (DOI: 10.1136/adc.2005.088872)