Children born early preterm score higher on ADHD symptom and inattention tests compared with children born at gestational week 40, according to research published in JAMA Pediatrics.
This population-based cohort study evaluated 113,227 children in Norway by comparing the results of a conventional cohort design with the results from a sibling-comparison design after adjusting for genetic and environmental factors. Analyses compared children and siblings in gestational age groups: early preterm, late preterm, early term, delivery at gestational week 39, delivery at week 40 (the reference group), delivery at week 41, and late term. The main measure was maternally reported ADHD symptoms in children age 5 and symptoms of inattention and hyperactivity/impulsivity in children age 8.
Researchers found that after accounting for unmeasured genetic and environmental factors, early preterm birth was associated with increased ADHD symptoms in preschool children and that early premature birth was associated with inattentive, but not hyperactive, symptoms in children age 8. In addition, there was a more significant association between gestational age and preschool ADHD symptoms in girls. Early preterm girls displayed more symptoms than their term-born sisters.
The study had several limitations. Participation rate was at 41%, which suggests a possible bias of non-random participation. Researchers found that young women, smokers, and women with low educational levels were under-represented. Attrition over time may have caused additional selection bias. Only exposure-discordant siblings were analyzed, and adjustment for unmeasured factors shared between siblings may have included variables that could introduce bias. Finally, maternal reports are not equivalent to psychiatric evaluations.
“This study demonstrates the importance of differentiating between inattention and hyperactivity/impulsivity and stratifying [based on] on sex in the study of childhood ADHD,” the researchers concluded. “The findings illustrate [the] potential gains of reducing preterm birth and the importance of providing custom support to children born preterm to prevent neurodevelopmental problems.”
Ask H, Gustavson K, Ystrom E, et al. Association of gestational age at birth with symptoms of attention-deficit/hyperactivity disorder in children [published online June 25, 2018]. JAMA Pediatrics. doi:10.1001/jamapediatrics.2018.1315