To assess the interaction between maternal attention-deficit/hyperactivity disorder (ADHD) history and young parental age on child's ADHD risk.
The study included 321,272 singleton children born between 1995 and 2012 from hospitals within a single integrated health care organization. The children were prospectively followed up through electronic medical record systems from birth until the first date of the following: date of clinical diagnosis of ADHD, last date of continuous health plan membership, death due to any cause, or December 31, 2017. Risks of ADHD associated with a maternal history of ADHD before pregnancy and young parental age were assessed by using Cox regression adjusting for potential confounders.
The children were followed up for a median (interquartile range) of 8.9 (6.2, 13.6) years from birth. Among them, 5.1% had ADHD diagnosis, 1.8% had a maternal history of ADHD before the pregnancy, and 4.4% had mothers <20 years and 2.3% had fathers <20 years at date of birth. The hazard ratio (HR) of ADHD in children associated with parental age <20 years varied by maternal history of ADHD (p < 0.005 for both multiplicative and additive interactions). For children without a maternal history of ADHD, the HR associated with at least 1 parent <20 years was 1.14 (95% confidence interval 1.04–1.24). However, for children with a maternal history of ADHD, the HR associated with at least 1 parent <20 years was 1.92 (95% confidence interval 1.31–2.82).
High ADHD risk in offspring associated with young parenthood was predominantly observed among children with a maternal history of ADHD.