Early life risk factors for attention-deficit/hyperactivity disorder: A population-based cohort study

OBJECTIVES: To identify risk factors for attention-deficit/hyperactivity disorder (ADHD) and to determine whether these factors differ between boys and girls. SUBJECTS AND METHODS: We conducted a case-control study of all children born between January 1, 1976, and December 31, 1982, in Olmsted County, Minnesota (N=5701), and examined birth certificates for risk factors for ADHD. Using school and medical records, we identified 305 children with ADHD. All children not identified with ADHD served as controls (N=5326). Risk factors that were assessed included demographic characteristics of both children and parents, as well as pregnancy, labor, and delivery characteristics, including the effect of a multiple birth and presence of pregnancy and delivery complications. RESULTS: Pregnancy and labor characteristics, low birth weight, and presence of a twin birth were not associated with ADHD. Male sex (adds ratio [OR], 3.05; 95% confidence interval [CI], 2.34-3.98) was associated with an increased risk for ADHD, whereas high maternal and paternal education levels (high maternal education: OR, 0.57; 95% CI, 0.42-0.78; high paternal education: OR, 0.58; 95% CI, 0.49-0.78) were associated with a decreased risk for ADHD. In addition, low maternal and paternal education levels increased the risk for ADHD in boys more than in girls. CONCLUSION: Male sex and low parental education levels are significant risk factors for ADHD. In addition, boys born to parents with low maternal and paternal education levels appear to be at an increased risk for ADHD compared with girls born to parents with low education levels.