The association between smoking during pregnancy and hypertensive disorders of pregnancy: A systematic review and meta-analysis

Background Smoking is a major public health problem. However, its association with hypertensive disorders of pregnancy (HDP) is inconclusive. Objective To find the association between smoking during pregnancy and HDP. Search strategy We searched PubMed, Ovid and Cochrane Library up to March, 2021, using terms including "smoking" and "HDP". Selection criteria Observational studies that assessed the relationship between smoking during pregnancy and HDP were included. Data collection and analysis Odds ratios (OR) and 95% confidence intervals (CI), and other necessary data were extracted. Stata16.0 MP was used to analyze statistics. Main results A total of 13 studies were included. Meta-analysis revealed that smoking during pregnancy was a protective factor for HDP (OR 0.78, 95% CI 0.67-0.92), gestational hypertension (OR 0.74, 95% CI 0.69-0.79), and pre-eclampsia (OR 0.65, 95% CI 0.58-0.73). Subgroup analysis showed that smoking during pregnancy was a risk factor for HDP in Asia but a protective factor in Europe and North America. Neither quitting smoking before pregnancy nor during pregnancy had a statistically significant association with HDP. Conclusion This meta-analysis revealed that smoking during pregnancy might prevent HDP, gestational hypertension, and pre-eclampsia. Smoking during pregnancy was a risk factor for HDP in Asia but a protective factor in Europe and North America.