Child behavior problems increased by maternal smoking during pregnancy

We investigated the effects of maternal smoking during pregnancy on behavio ral problems (i.e., not mediated by low birth weight) in 3-y-old offspring. We assessed behavioral problems in 1 377 2- to 3-y-old twin pairs (registe red in the Netherlands Twin Register) with the Child Behavior Checklist for ages 2-3 y (CBCL/2-3) from Achenbach, Edelbrock, and Howell. Two to 3 y ea rlier (i.e., soon after the birth of the twins) we collected information ab out the smoking habits (i.e., "never," "sometimes," and ''regularly") of th e mother during pregnancy. We analyzed the effect of maternal smoking on th e CBCL total score and on several subscale scores for first- and second-bor n twins separately, and we adjusted for the possible confounding effects of birth weight, socioeconomic status, maternal age, and type of feeding (i.e ., breast or bottle fed). There was a significant effect of maternal smokin g on so-called ''externalizing" behavioral problems (e.g., oppositional, ag gressive, overactive), but not on "internalizing" behavioral problems (e.g. , withdrawn, depressed, anxious), in both first- and second-born twins. The enhanced "externalizing" problems were attributed predominantly to increas ed aggression. Although boys have higher externalizing and aggression score s than girls, the effect of maternal smoking was the same for boys and girl s.