An intercontinental comparison of the influence of smoking on the occurrence of nonsyndromic cleft lip and palate: a meta-analysis and systematic review.

Background: The influence of smoking on nonsyndromic clefts has been a topic of research for many years. However, few studies have investigated the effect of smoking on causing clefts in different gene pools.

Methods: A meta-analysis was conducted of case-control studies related to smoking. Keywords such as "clefts," "cleft lip," "cleft palate," "orofacial cleft," and "smoking" were used to search the MEDLINE, Embase, and Cochrane databases.

Results: In total, 51 articles were reviewed. The RevMan software was utilized for the analysis, and the Mantel-Haenszel method was employed to pool the odds ratios (ORs) and 95% confidence intervals. Although the overall OR, a measure of the association between exposure and outcome, was higher for smokers than for non-smokers, this association was significantly stronger in individuals from Asia and South America (1.73), and lowest in Europe (1.31). Among active and passive smokers in Asia, the OR was approximately 0.93, indicating an equivalent impact from both types of smoking.

Conclusion: This analysis indirectly suggests that restriction measures targeting both active and passive smoking are crucial in Asia.