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OBJECTIVE: Maternal smoking during pregnancy may increase the risk for behavioral disorders. The aim of this study was to investigate the association between smoking during pregnancy and hyperkinetic and attention-deficit/hyperactivity disorder in the offspring in a large population-based study. METHODS: This study was designed as a nested case-control study. Data were obtained from Danish longitudinal registers and included 170 children with hyperkinetic disorder and 3765 population-based control subjects, who were matched by age, gender, and date of birth. Potential confounders, including newborn characteristics, socioeconomic status, and family history of psychiatric illnesses, were evaluated by conditional logistic regression analyses. RESULTS: Women who smoked during pregnancy had a 3-fold increased risk for having offspring with hyperkinetic disorder compared with nonsmokers. Socioeconomic factors and history of mental disorder in the parents or siblings seemed to confound the result to some extent (adjusted relative risk: 1.9; 95% confidence interval: 1.3-2.8). Adjustment for parental age or exclusion of children with low birth weight (<2500 g), preterm delivery (<37 weeks completed gestation), and Apgar scores <7 at 5 minutes revealed no changes in the results. Also, excluding children with conduct disorders or comorbid disorders revealed no change in the results. CONCLUSIONS: Our results showed an increased risk for hyperkinetic disorder in children of mothers who smoked during pregnancy. This could not be explained by newborn characteristics, parental socioeconomic status, family history of psychiatric hospitalizations or contact as outpatients, conduct disorders, or comorbidity.
Linnet et al. (Mon,) studied this question.