June 28, 2018
Early premature birth may result in higher levels of attention deficit disorder (ADHD or ADD) symptoms in preschool and school-age children, even after accounting for genetic and environmental factors, according to a new study of children born before the gestational age of 34 weeks published recently in JAMA Pediatrics1.
Using a sibling-comparison approach, researchers from the Norwegian Institute of Public Health in Oslo conducted a prospective, population-based cohort study to examine whether gestational age at birth and symptoms of ADHD are correlated at five and eight years of age, and if there are sex differences in the associations.
The researchers studied 113,227 children (48.7% girls; 28.0% born at gestational week 40), including 33,081 siblings (48.4% girls; 29.3% born at gestational week 40. For the 5-year-old children, ADHD symptoms were assessed using the Conner’s Parent Rating Scale–Revised; for the 8-year-old-children, symptoms of inattention and hyperactivity/impulsivity were measured using the Parent/Teacher Rating Scale for Disruptive Behavior Disorders. Both questionnaires reflected ADHD criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV).
After adjusting for pregnancy-specific factors, and compared with their siblings born in gestational week 40, children who were born in gestational weeks 22-33 scored 0.32 standard deviations (SD) higher on the ADHD scales at five years of age and 0.31 SD higher for inattention at eight years. They scored 0.03 SD lower for hyperactivity at eight years of age. The corresponding odds ratios were 1.79 on ADHD at five years of age, 1.75 on inattention at eight years of age, and 0.95 on hyperactivity at eight years of age.
Researchers found a strong association between gestational age and preschool ADHD symptoms among girls. Early premature girls scored a mean of 0.8 SD higher compared with their term-born sisters (P =.02), corresponding to an odds ratio of 4.27.
Sibling-comparison design is “perhaps the closest you get to an experiment,” lead researcher Helga Ask, Ph.D., told Medpage Today. “We found that the observed association between being born premature and ADHD symptoms in childhood was not explained by genetic or environmental factors shared between siblings. In other words, the association appears to be of a causal nature.”
Limitations of this study included a low participation rate (41%). Furthermore, young women, smokers, and women with low educational level were underrepresented.
This study showed that “differentiating between dimensions of inattention and hyperactivity/impulsivity, as well as by sex, can provide important knowledge about ADHD,” concluded the authors. “The findings illustrate potential gains of reducing preterm birth and the importance of providing custom support to children born preterm to prevent neurodevelopmental problems.”
1Ask H, Gustavson K, Ystrom E, et al. “Association of Gestational Age at Birth With Symptoms of Attention-Deficit/Hyperactivity Disorder in Children.” JAMA Pediatrics online, 25 June 2018. doi:10.1001/jamapediatrics.2018.1315