Ask H, et al. - The relationship between gestational age at birth and symptoms of attention-deficit/hyperactivity disorder (ADHD) in preschool and school-age children after adjusting for unmeasured genetic and environmental risk factors was investigated in this prospective, population-based cohort study. Researchers reported that early preterm birth was correlated with a higher level of ADHD symptoms in preschool children after accounting for unmeasured genetic and environmental factors. In 8-year-old children, early premature birth was correlated with inattentive but not hyperactive symptoms. The importance of differentiating between inattention and hyperactivity/impulsivity and stratifying on sex in the study of childhood ADHD was showed.

Methods

• From January 1, 1999, through December 31, 2008, pregnant women were enrolled from across Norway.
• Using data from the Norwegian Mother and Child Cohort Study, results of a conventional cohort design were compared with results from a sibling-comparison design (adjusting for genetic and environmental factors shared within families).
• From October 1, 2017, through March 16, 2018, data analysis was performed.
• Analyses compared children and siblings discordant for gestational age group: early preterm (delivery at gestational weeks 22-33), late preterm (delivery at gestational weeks 34-36), early term (delivery at gestational weeks 37-38), delivery at gestational week 39, reference group (delivery at gestational week 40), delivery at gestational week 41, and late term (delivery after gestational week 41).
• Maternally reported symptoms of ADHD in children at 5 years of age and symptoms of inattention and hyperactivity/impulsivity at 8 years of age were the main outcomes and measures.
• Covariates included child and pregnancy characteristics correlated with the week of delivery and the outcomes.

Results

• An aggregate of 113,227 children (55,187 [48.7%] female; 31,708 [28.0%] born at gestational week 40), including 33,081 siblings (16,014 female [48.4%]; 9705 [29.3%] born at gestational week 40), were involved in the study.
• As compared to 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 SD (95% CI, 0.14-0.34) higher on ADHD symptom tests, 0.33 SD (95% CI, 0.24-0.42) higher on inattention tests, and 0.23 SD (95% CI, 0.14-0.32) higher on hyperactivity/impulsivity tests compared with children born at gestational week 40 after adjusting for unmeasured genetic and environmental factors.
• Findings revealed that sex moderated the association of gestational age with preschool ADHD symptoms.
• Among girls, the association appeared to be strongest.
• According to the findings obtained, early preterm girls scored a mean of 0.8 SD (95% CI, 0.12-1.46; P=.02) higher compared with their term-born sisters.