Background: ADHD is a common disorder affecting 5% of children worldwide. Many previous studies have examined associated risk factors of ADHD, but the aetiology of ADHD still remains multifactorial and inconclusive. Our study examined perinatal environmental risk factors of ADHD children in a sibling control study.
Method: We collected data of 130 ADHD-sibling pairs; ADHD children who met the DSM IV for ADHD and had been on stimulant medication for at least a year while their siblings closest in age without ADHD were selected for comparison. We utilized a sibling design to control for shared genetic and environmental factors.
Results: The ADHD subjects were similar to controls for birth weight, gestation, mean age and the occurrence of maternal postnatal depression; but significantly different in gender ratio. Adverse events in pregnancy were reported more commonly in the ADHD group than the sibling group. Smoking and alcohol use in pregnancy were similar in both groups. Siblings without ADHD were more likely to be delivered by spontaneous delivery (p = 0.044) and ADHD children more likely to require induction (p = 0.014).
Conclusion: Children with ADHD and their siblings were equally exposed to risk factors such as smoking and alcohol in utero, popularly thought to be implicated in ADHD aetiology. Risk factors previously thought to be associated with ADHD need to be re-examined through intra-familiar studies adequately controlling for confounding factors.