Maternal Smoking and Risk of Hypertensive Disorders of Pregnancy: Effect Modification by Body Mass Index and Gestational Weight Gain.

Background: Although smoking cigarettes has been shown to have a protective effect on preeclampsia, quitting smoking also results in weight gain. Weight gain leading to an obese body mass index is a risk factor for hypertensive disorders of pregnancy (HDP).

Methods: The objective of this study was to explore the relationship between smoking status, body mass index, and gestational weight gain on the risk of HDP. A cross-sectional analysis was performed utilizing US birth certificate data. We examined HDP risks in relation to maternal smoking, body mass index, and gestational weight gain. Associations were expressed as rate ratios with 95% CIs and adjusted for potential confounders. Clinically important outcomes of smoking throughout pregnancy were also evaluated.

Results: Of the 22 191 568 women studied, HDP rates among nonsmokers, those who quit smoking, and persistent smokers were 6.8%, 8.6%, and 7.0%, respectively. The rate ratio of HDP was higher for women who quit smoking, especially evident among those with excessive gestational weight gain. Corrections for exposure misclassification and unmeasured confounding strengthened the associations among women who quit smoking. There was an almost 6-fold increase in the rate of stillbirth for persistent smokers (2.3%) compared with those who quit smoking (0.4%) and nonsmokers (0.4%).

Conclusions: Women who quit smoking during pregnancy were more likely to gain excessive weight and develop HDP. Although quitting smoking during pregnancy may be associated with an increase in the risk of HDP, it is also associated with a reduced risk of stillbirth. Pregnant women counseled to quit smoking should also receive counseling on nutrition and exercise to prevent excessive gestational weight gain.