A recent study has found that the link between low fetal growth rate and symptoms of attention-deficit/hyperactivity disorder (ADHD) in children can partially be explained by factors occurring before birth such as pregnancy complications, in addition to familial characteristics such as household income. The findings were published in Research on Child and Adolescent Psychopathology.
ADHD is a common neurodevelopmental disorder developing in childhood. Symptoms include difficulty paying attention, hyperactivity, and impulsive behavior. Previous research has uncovered several risks for the development of ADHD symptoms in childhood, including genetics, being male, and restricted fetal growth rate.
Fetal growth rate is partially determined by the environment the fetus develops in prior to birth. Therefore the study team, led by Niamh Dooley from the Royal College of Surgeons in Ireland, esd interested in unveiling how much of the link between fetal growth rate and ADHD could be explained by differing environmental aspects – prenatal (before birth) factors, as well as familial factors.
To investigate this, the researchers analyzed data from two independent studies: the Adolescent Brain Cognitive Development (ABCD) study from the USA, and the Growing Up in Ireland (GUI) study. The American study followed 8,835 participants while the Irish study followed 7,724 participants over a few years, with both studies using standard questionnaires to assess ADHD symptoms when the participants were aged 9 to 10 years old (born between 2007 and 2009).
The studies collected information on prenatal factors, which encompassed pregnancy complications (e.g. persistent nausea/vomiting, high blood pressure and gestational diabetes), in addition to data on maternal smoking, alcohol consumption and drug use.
Familial factors were also investigated, including race/ethnicity, maternal age, familial income, parental education level, single parenthood, and family psychiatric history.
After data cleaning and statistical analyses, Dooley and colleagues discovered that over a quarter of the association between fetal growth and ADHD symptoms is attributable to familial factors (30.2% in the American group and 26.6% in the Irish group).
Interestingly, the degree to which the association was explained by prenatal factors differed by the study group.
Pregnancy complications explained a larger proportion of the effect in the USA (7.9%), compared to Ireland at (2.7%). “While we did not assess interactive effects between pregnancy complications and maternal age, the younger age of [American] mothers compared to [Irish mothers] may explain the difference in results… Alternatively, this result may be explained by unmeasured [group] differences such as in maternal weight status, stress access to prenatal care, or quality of care,” the authors explain.
Meanwhile, maternal substance use had a greater impact in Ireland (22.7%) compared to the USA (4.8%). The researchers noted, “Our findings are consistent with another analysis of the [Irish] data which showed strong links between maternal smoking and intrauterine growth restriction in Ireland and support the need for improved smoking cessation programs in Irish maternal hospitals”.
“Given reliable associations between fetal growth and ADHD symptoms have been observed in human and animal studies, it may be that maternal substance use in pregnancy, such as smoking, impacts child neurodevelopment via fetal growth restriction,” Dooley and colleagues concluded.
While these findings provide valuable insights into how various components contribute to ADHD symptoms, the authors note that different scales and definitions were used in the American and Irish studies when capturing data, and suggest that future studies could find groups that have better-matched data. Additionally, other characteristics may have influenced the data that were not measured, including migrant status and neighborhood poverty.
The study, “Explaining the Association Between Fetal Growth and Childhood ADHD Symptoms: Cross‑cohort Replication”, was authored by Niamh Dooley, Colm Healy, Ross Brannigan, David Cotter, Mary Clarke and Mary Cannon.