Objective To examine the association between ischemic-hypoxic conditions (IHC) and Attention Deficit Hyperactivity Disorder (ADHD) by gestational age at delivery and race/ethnicity.
Methods A nested case-control study using the Kaiser Permanente Southern California (KPSC) medical records. Study cohort were children aged 5–11 years who were delivered and cared for in KPSC Healthcare system between 1995–2010 (n =308,634). Cases were children with a clinical diagnosis of ADHD and obtained at least 2 prescriptions specific to ADHD during the follow-up period. For each case, five controls matched to cases on child age at time of diagnosis were selected. Exposures were defined based on ICD-9 codes. A conditional logistic regression model was used to estimate adjusted odds ratios (OR).
Results Among eligible children, 13,613 (4.3%) had a diagnosis of ADHD. Compared to control children, case children were more likely to be male and of White or African-American race/ethnicity. Case children than controls were more likely to be exposed to IHC (OR=1.16, 95% confidence intervals [CI] 1.11–1.21). Analysis of cases and controls stratified by gestational age revealed that case children born at 28–33, 34–36, and 37–42 weeks of gestation, were significantly more likely to be exposed to IHC; 1.6-fold (95% CI, 1.2–2.2), 1.2-fold (95% CI, 1.0–1.4), and 1.1-fold (95% CI, 1.0–1.2), respectively, compared to control children. IHC was associated with increased odds of ADHD across all race/ethnicity groups.
Conclusion These findings suggest that IHC is independently associated with an increased risk of childhood ADHD especially in early preterm birth.