Congenital malformations are associated with secondhand smoke among nonsmoking women: A meta-analysis.

Background: The association between active maternal smoking and congenital malformations is well established, but little is known about the association between secondhand smoke and congenital malformations. Moreover, studies regarding the association between congenital malformations and secondhand smoke have not yielded consistent results.

Methods: In July 2018, we searched PubMed, EMBASE, and China Biology Medicine databases for observational studies characterizing the relationship between secondhand smoke and congenital malformations of offspring in nonsmoking women. Two reviewers independently decided on whether a study should be included, did data extraction, and assessed study quality. Pooled risks with 95% confidence intervals were calculated using either the fixed-effects models or random-effects models. Further subgroup analyses and sensitivity analyses were performed to explore the potential source of heterogeneity and to examine the robustness of risk estimates.

Results: Thirty-three studies with a total of 31 944 cases and 32 335 controls were included. Secondhand smoke exposure was associated with an increased risk of congenital malformations (odds ratio = 1.92; 95% confidence interval 1.61-2.30). Secondhand smoke was correlated with significantly increased risk for digestive system (1.17 [1.05-1.32]), nervous system (1.74 [1.33-2.29]), and cardiovascular system (2.10 [1.32-3.35]) malformations and for oral clefts (1.87 [1.47-2.39]).

Conclusions: Secondhand smoke exposure increases the risk for overall and several organ-system malformations. These findings highlight the necessity of improving community awareness to prevent secondhand smoke exposure during the preconception and conception periods.