According to the findings, children born close to term at 34 to 36 weeks had a 70% increased risk of developing hyperkinetic disorder (RR 1.7, 95% CI 1.2 to 2.5). Babies born before 34 complete weeks had an almost three-fold increased risk (RR 2.7, CI 1.8-4.1), the researchers reported.
Babies born at term but with low birth weights were also at risk of hyperkinetic disorder. Compared with babies having a birth weight above 2,999 g, term-babies weighing only 1,500 -2,499 g had a 90% increased risk (RR 1.9 CI 1.2-2.9).
Finally, even those with marginally lower birth weights-2,500-2,999 g-- had a 50% increased risk (RR 1.5 CI 1.2-1.8). Results were unchanged even after adjusting for differences in gestational ages, the investigators said.
Single parenthood, social and economic deprivation, and young age of the parents were all risk factors for hyperkinetic disorder, the investigators said. However, the results held even after adjusting for these factors as well as for parents' socioeconomic status, family history of psychiatric disorders, conduct disorders, comorbidity, and maternal smoking during pregnancy.