Smoking and orofacial clefts: a United Kingdom–based case-control study

Objective: To investigate the association between smoking and orofacial clefts in the United Kingdom. Design: Case-control study in which the mother's exposure to tobacco smoke was assessed by a structured interview. Setting: Scotland and the Manchester and Merseyside regions of England. Participants: One hundred ninety children born with oral cleft between September 1, 1997, and January 31, 2000, and 248 population controls, matched with the cases on sex, date of birth, and region. Main Outcome Measure: Cleft lip with or without cleft palate and cleft palate. Results: There was a positive association between maternal smoking during the first trimester of pregnancy and both cleft lip with or without cleft palate (odds ratio 1.9, 95% confidence interval 1.1 to 3.1) and cleft palate (odds ratio 2.3, 95% confidence interval 1.3 to 4.1). There was evidence of a dose-response relationship for both types of cleft. An effect of passive smoking could not be excluded in mothers who did not smoke themselves. Conclusion: The small increased risk for cleft lip with or without cleft palate in the offspring of women who smoke during pregnancy observed in this study is in line with previous evidence. In contrast to some previous studies, an increased risk was also apparent for cleft palate. In these U.K. data, there was evidence of a dose-response effect of maternal smoking for both types of cleft. The data were compatible with a modest effect of maternal passive smoking, but the study lacked statistical power to detect or exclude such an effect with confidence. It may be useful to incorporate information on the effects of maternal smoking on oral clefts into public health campaigns on the consequences of maternal smoking.