Smoking and placenta previa: a meta-analysis.

OBJECTIVE: Previous studies found a positive association between placenta previa and smoking during pregnancy. However, the results of these studies are inconsistent. The aim was to perform meta-analysis of the association between smoking during pregnancy and placenta previa.

METHODS: Major electronic databases, including PubMed, Web of Science, and Scopus were searched until June 2015. The heterogeneity across studies was explored by Q-test and I2 statistic. The possibility of publication bias was assessed using Begg's and Egger's tests. The results were reported using odds ratio (OR) estimate with its 95% confidence intervals using a random-effects model.

RESULTS: The literature search yielded 991 publications until October 2015 with 9,094,443 participants. Based on the random effect model, compared to nonsmoker women, the estimated OR and RR of placenta previa was 1.42 (95% CI: 1.30, 1.54) and 1.27 (95% CI: 1.18, 1.35), respectively.

CONCLUSIONS: There is sufficient documents based on the observational studies that smoking during pregnancy is significantly associated with an increased risk of placenta previa. Therefore, smoking during pregnancy can be considered as a predictor of placenta previa.