The researchers estimated the mothers’ exposures to nitrogen oxides (NOx) and particulate matter (PM10 and PM2.5) throughout pregnancy at their home address and assessed the children’s ADHD symptoms using questionnaires completed by parents and/or teachers.

The team classified a total of 2,801 children as having ADHD symptoms within the borderline/clinical range and 1,590 within the clinical range.

However, they found no evidence of a link between exposure to air pollution during pregnancy and a higher risk of ADHD symptoms within either the borderline or clinical range.

Although previous research has suggested that prenatal exposure to air pollution may affect brain development and increase attention-deficit/ hyperactivity disorder (ADHD) symptoms in children, the findings so far have been inconsistent.

“Given the conclusions of this study and the inconsistent findings of previous studies, we hypothesize that exposure to air pollution might not increase the risk of ADHD in children in the general population,” said ISGlobal researcher Mònica Guxens, who coordinated the study.

“However, we believe that exposure to air pollution could have harmful effects on neuropsychological development, especially in genetically susceptible children.”

With a worldwide prevalence of 5%, ADHD is the most common childhood behavioral disorder. Symptoms include inattention, hyperactivity and/or impulsivity which can interfere with a child’s development and academic performance.

It has previously been shown that ADHD is the result of complex interactions between genetic background — heritability is approximately 75% — and environmental and factors.

The results can be found published online in the journal Epidemiology.