Maternal smoking during pregnancy and child behaviour problems: the Generation R Study

Background Several studies showed that maternal smoking in pregnancy is related to behavioural and emotional disorders in the offspring. It is unclear whether this is a causal association, or can be explained by other smoking-related vulnerability factors for child behavioural problems. Methods Within a population-based birth cohort, both mothers and fathers reported on their smoking habits at several time-points during pregnancy. Behavioural problems were measured with the Child Behavior Checklist in 4680 children at the age of 18 months. Results With adjustment for age and gender only, children of mothers who continued smoking during pregnancy had higher risk of Total Problems [odds ratio (OR) 1.59, 95% confidence interval (CI): 1.21-2.08] and Externalizing problems (OR 1.45, 95% CI: 1.15-1.84), compared with children of mothers who never smoked. Smoking by father when mother did not smoke, was also related to a higher risk of behavioural problems. The statistical association of parental smoking with behavioural problems was strongly confounded by parental characteristics, chiefly socioeconomic status and parental psychopathology; adjustment for these factors accounted entirely for the effect of both maternal and paternal smoking on child behavioural problems. Conclusions Maternal smoking during pregnancy, as well as paternal smoking, occurs in the context of other factors that place the child at increased developmental risk, but may not be causally related to the child's behaviour. It is essential to include sufficient information on parental psychiatric symptoms in studies exploring the association between pre-natal cigarette smoke exposure and behavioural disorders.