Maternal smoking and the risk of congenital birth defects: a cohort study.

BACKGROUND The literature linking gestational smoking to congenital defects has been very inconsistent. The purpose of this study was to reinvestigate the relation between gestational smoking and congenital malformations. METHODS This study was a retrospective cohort (N = 18,016) of live births in the TriHealth Hospital system from 1 January 1998 to 31 December 1999. The cohort included 1,943 mothers who were smokers. Congenital defects were grouped into 22 different categories. Multifactorial logistic regression was used to find any association between exposure and the possible outcomes. RESULTS Mothers who smoked were significantly younger and had babies of lower birth weight and shorter gestational age (P < .05). Of the 22 categories of congenital defects, only cardiovascular system abnormalities showed a significant difference (P < .01) between the two groups. The remaining 21 categories of congenital defects showed no statistical difference. CONCLUSION Women who smoke during pregnancy have infants that are significantly smaller and of shorter gestational age compared with mothers who do not smoke. Based on these data and findings from most of the available literature, however, gestational smoking is unlikely to cause a large increase in congenital birth defects.