Children born early preterm (gestational age 22-33 weeks) scored an average of 0.24 SD higher than children born full term. For girls, this increased to 0.8 SD higher than term born sisters.
Helga Ask, PhD
Early preterm birth—delivery at gestational age 22-33 weeks—is associated with a higher level of ADHD symptoms in preschool-age children, according to a decade-long prospective cohort study of siblings in Norway. Children who were born early preterm scored an average of 0.24 SD (95% CI, 0.14-0.34) higher on ADHD symptoms at age 5 compared with children born at 40 weeks gestational age.
“The findings illustrate potential gains of reducing preterm birth and the importance
of providing custom support to children born preterm to prevent neurodevelopmental problems,” said the study authors Helga Ask, PhD, Kristin Gustavson, PhD, Eivind Ystrom, PhD, et al.
The study also found that early premature birth was associated with inattentive, but not hyperactive ADHD symptoms in children at 8 years of age. Compared to siblings born at 40 weeks, children born early preterm scored 0.32 SD D (95% CI, 0.02-0.62) higher on ADHD at 5 years of age, 0.31 SD (95% CI, 0.05-0.57) higher on inattention at 8 years of age, and 0.03 (95% CI, −0.32 to 0.26) lower on hyperactivity at 8 years of age.
“To our knowledge, this is the first study to investigate the association between preterm birth and symptoms of ADHD using a sibling-comparison design,” said the authors.
The study was comprised of 113,227 children (48.7% female; 28.0% born at gestational week 40), including 33,081 siblings (48.4% female; 29.3% born at gestational week 40). Data came from the Norwegian Mother and Child Cohort Study conducted by the Norwegian Institute of Public Health. Pregnant women were recruited from 1999 through 2008 from across Norway, with a participation rate of 41%.
Mothers participating in the study completed 12 items of the Conner’s Parent Rating Scale-Revised, which reflects the criteria for ADHD in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), for their children at age 5. When children were 8 years old, symptoms were measured using items from the Parent/Teacher Rating Scale for Disruptive Behavior Disorders related to ADHD. Nin symptoms of inattention and 9 symptoms of hyperactivity/impulsivity were rated on a 4-point scale.
Results showed a sex by gestational week interaction effect on ADHD symptoms when children were 5 years old. Girls born at gestational age 22-33 weeks scored a mean of 0.8 SD higher compared to their sisters born at full term (95% CI, 0.12-1.46; P = .02). This association between gestational age and ADHD symptoms at 5 years of age was not observed in boys when compared to their brothers.
“Our results suggest that the negative consequences of being born preterm are most pronounced in girls (at 5 years of age), although the power of the sex-stratified analyses is limited,” said study authors. “A high score on inattention might be a reflection of related constructs, for example, anxiety, which is more prevalent among girls than boys, a possible explanation for the observed sex difference.”
Study authors emphasized the benefit of a sibling-comparison design for studying ADHD symptoms as well as the benefits of differentiating between inattentive and hyperactive/impulsive behaviors and between sex.
The study, “Association of Gestational Age at Birth With Symptoms of Attention-Deficit/Hyperactivity Disorder in Children,” was published online in JAMA Pediatrics.