Maternal smoking and the risk for clubfoot in infants.

Background: Clubfoot is one of the most common major birth defects, with a prevalence of approximately 1 per 1,000 live births. The etiology of clubfoot is complex and not well understood, and yet, few epidemiologic studies of risk factors have been conducted. Maternal smoking has been suggested as a possible risk factor. The purpose of this population-based, case-control study was to examine the association between maternal smoking and clubfoot.

Methods: Data from the North Carolina Birth Defects Monitoring Program matched to North Carolina birth certificates and health services data were used in the analysis of 443 cases of clubfoot and 4,492 randomly sampled controls for the years 1999-2003. Smoking data were ascertained from the birth certificates, and the reliability of the data was assessed by comparing them with reported smoking from the North Carolina Pregnancy Risk Assessment Monitoring System. Multiple logistic regression was used to calculate crude and adjusted ORs and 95% CIs for smoking and clubfoot.

Results: The crude OR for maternal smoking during pregnancy and clubfoot was 1.49 (95% CI: 1.15, 1.92). Controlling for maternal age, race/ethnicity, infant's sex, and timing of prenatal care initiation did not appreciably change the results (adjusted OR 1.40; 95% CI: 1.07, 1.83).

Conclusions: This study is consistent with the hypothesis that smoking during pregnancy is associated with a slightly increased risk of an infant being born with clubfoot. Further research is needed to confirm this association, and to identify potential genetic factors that may modify the magnitude of the risk.