Is there an association between maternal smoking and oral clefts?

Data sourcesCochrane, PubMed and Ovid Medline. A search timeline of January 1966 to May 2015 was used and language was restricted to English.Study selectionCase-control and cohort studies relating to oral clefts, with information on maternal active smoking, before and after conception, excluding paternal smoking and exposure to environmental tobacco smoke.Data extraction and synthesisTwo authors extracted data independently. Both Begg's and Egger's funnel plots were used to assess publication bias. Sensitivity analysis was performed to assess impact of the different study types and chi-squared and P values were determined by SPSS software. Studies with missing data were excluded from the meta-analysis.ResultsA statistically significant association was found between maternal active smoking and CL +/- P (odds ratio [OR] 1.368; 95% confidence interval [CI] 1.259-1.486) as well as CP (OR 1.241; 95% CI 1.117-1.378). Half the studies showed positive dose-response effect for each subgroup (test for linear trend, P < .05).ConclusionsWomen who smoke during pregnancy have a moderate risk of having a child with a CL +/- P or CP. A dose-response effect between maternal smoking and clefts was not established.