Meta-analysis of the association of maternal smoking and passive smoking during pregnancy with neural tube defects

BackgroundIt is unclear whether the incidence of neural tube defects (NTDs) is greater with maternal smoking or with passive smoking during pregnancy. ObjectivesTo compare the effects of smoking and passive smoking during pregnancy on the risk of NTDs. Search strategyEnglish and Chinese databases were searched for relevant papers published before March 2017, using search terms including smoking and NTD. Selection criteriaCase-control and cohort studies on the aforementioned association were included. Data collection and analysisTwo authors independently extracted the original data. Meta-analyses were performed to assess the risks associated with smoking and passive smoking, followed by a comparison of the two pooled effect estimates. The I-2 statistic was used to examine between-study heterogeneity. Main resultsThe final analysis included 23 articles representing 33 studies. The pooled odds ratio (OR) and 95% confidence interval (CI) for the risk of NTDs was 1.052 (0.907-1.220) with smoking and 1.898 (1.557-2.313) with passive smoking. Comparison of these ORs indicated that the risk of NTDs was higher with passive smoking than with smoking (OR 1.804, 95% CI 1.409-2.309). ConclusionsCompared with smoking, exposure to passive smoking during pregnancy carries a higher risk of having infants with NTDs. Compared with women who smoke during pregnancy, women exposed to passive smoking during pregnancy have a higher risk of having infants with neural tube defects.