(HealthDay)—Early preterm birth is associated with a higher level of attention deficit/hyperactivity disorder (ADHD) symptoms in preschool children after accounting for unmeasured genetic and environmental factors, according to a study published online June 25 in JAMA Pediatrics.

Helga Ask, Ph.D., from the Norwegian Institute of Public Health in Oslo, and colleagues recruited pregnant women in a prospective, population-based cohort study. The correlation between gestational age at birth and symptoms of ADHD in preschool and school-age children was compared after adjustment for unmeasured genetic and . Data were included for 113,227 children, including 33,081 siblings who were part of a sibling-comparison design.

The researchers found that compared with term-born children, children born early preterm were rated with more symptoms of ADHD, inattention, and hyperactivity/impulsivity. Children born early preterm had a mean score that was 0.24, 0.33, and 0.23 standard deviation (SD) higher on ADHD symptom tests, inattention tests, and hyperactivity/impulsivity tests, respectively, than children born at gestational week 40 after adjustment for unmeasured genetic and . The correlation of with preschool ADHD symptoms was moderated by sex, with the association strongest among girls. Compared with their term-born sisters, early preterm girls scored a mean of 0.8 SD higher.

"This study demonstrates the importance of differentiating between inattention and hyperactivity/impulsivity and stratifying on sex in the study of childhood ADHD," the authors write.

More information: Abstract/Full Text

Journal information: JAMA Pediatrics