Cigarette smoking during pregnancy is associated with a lower risk of preeclampsia, whereas obesity increases the risk of preeclampsia. We sought to assess the combined effect of smoking and obesity on the risk of preeclampsia.Methods
We conducted a population-based cohort study of 129,674 women who delivered singleton infants during 2000–2001. Data for cigarette use, pre-pregnancy body mass index (BMI), preeclampsia, and potential con-founders were obtained from birth certificate files. Man-tel-Haenszel stratified analysis and logistic regression were used to analyze the data.Results
The preeclampsia risk was 3.1, 4.5, 7.6 and 8.8% for normal weight (BMI 18.5–24.9), overweight (25.0–29.9), obese (30.0–39.9) and morbidly obese (≥40.0 kg/m2) women, respectively, who smoked cigarettes while pregnant. The preeclampsia risk was 3.9, 6.2, 9.0 and 12.3% for the same groups of women, respectively, who did not smoke during their pregnancy. Compared to non-smokers, the relative risk of preeclampsia for women who smoked cigarettes was 0.78 (95% confidence interval 0.73–0.83) before and after adjusting for pre-pregnancy BMI and other factors associated with preeclampsia.Conclusion
The risk of preeclampsia is lower for women who smoke cigarettes while pregnant regardless of their pre-pregnancy BMI.