Objective: The purpose of this study was to evaluate the relationship between maternal cigarette smoking and the risk of having an offspring with an oral cleft.
Design: This was a large population-based, matched case-control study derived from the United States Natality database for 1997.
Subjects: The sample consisted of 2029 cases with non-syndromic oral clefts and 4050 non-malformed controls. Controls were matched to cases on mother's and father's race and child's sex, county of birth, and month of birth. This sample was selected from a total of 3,093,821 births in the United States, which represents 80% of all births in this country during 1997.
Results: The association between maternal cigarette smoking and oral clefts in the offspring was close to the null (odds ratio 1.16; 95% confidence interval (CI) 1.01 to 1.33; one-sided Fisher exact test p =.0207). The comparison and pooling of results to those of a similar study that used the U.S. Natality database for 1996 resulted in a common Mantel-Haenszel odds ratio of 1.33 (95% CI 1.21 to 1.46). The dose-response analysis was slightly significant for all levels of maternal smoking.
Conclusion: This large study confirms that smoking during pregnancy is only a minor risk factor for oral clefting in the offspring.