Prenatal smoking and childhood behavior problems: is the association mediated by birth weight?

Maternal smoking during pregnancy is associated with both reduced birth weight and adverse neurobehavioral outcomes. The aim of this study was to investigate longitudinal associations between maternal smoking during pregnancy and childhood behavioral outcomes, and to determine the role of birth weight in mediating such associations. The study included 489 mother-child pairs. Prenatal exposures were assessed via maternal interviews conducted on average 1 year after delivery and child behavior assessments were completed at 5-12 years of age using the Child Behavior Checklist (CBCL) and Teacher Report Form (TRF). Maternal smoking during pregnancy was associated with externalizing and total behavior problems according to both mother and teacher report. Maternal smoking was also associated with the following percentage increases in scores: 41% (CBCL) and 44% (TRF) for aggressive behavior and 65% (CBCL) and 47% (TRF) for attention problems. Associations with behavior problems were attenuated or no longer observed for mothers that quit smoking in early pregnancy. The proportion of the total effect of maternal smoking on behavioral outcomes explained by differences in birth weight was small and ranged from 6.6% for externalizing behavior on the CBCL to 20.1% for rule-breaking behavior on the CBCL. Our results suggest that birth weight differences explain only a small proportion of the magnitude of association between maternal smoking during pregnancy and selected behavioral outcomes.