Maternal passive smoking during pregnancy and neural tube defects in offspring: a meta-analysis.

PURPOSE: This study aims to examine the association between maternal passive smoking during pregnancy and the occurrence of neural tube defects (NTDs) in offspring. METHODS: We retrieved studies published on the association between maternal passive smoking during pregnancy and the occurrence of NTDs in offspring. Meta-analysis was applied to calculate the pooled effect estimates and their 95% confidence intervals (CIs) using data from 10 case-control studies. The publication bias was assessed by the Egger's regression asymmetry test and Begg's rank correlation test with Begg's funnel plot. RESULTS: The pooled effect estimate of maternal passive smoking was 1.82 (95% CI 1.46-2.27) for total NTDs; the effect estimates were 1.72 (95% CI 1.44-2.06), 1.52 (95% CI 1.29-1.79), and 2.32 (95% CI 1.34-4.01) for NTDs subtypes of anencephaly, spina bifida and encephalocele, respectively. Stratified by geographic region of the studies, the pooled effect estimates were 2.11 (95% CI 1.46-3.06), 1.65 (95% CI 1.16-2.34), 1.25 (95% CI 0.41-3.80) in China, USA and Iran, respectively. CONCLUSIONS: This meta-analysis suggested that maternal passive smoking during pregnancy was associated with an increased risk of total NTDs and three NTDs subtypes in offspring. Specifically, the associations were also found to be significantly positive both in China and USA.