The relationship between smoking and the risk of pregnancy-induced hypertension (PIH) is not clearly established. Therefore, we conducted an analysis of cigarette smoking in a Polish cohort of women, recruited in the first trimester of a single pregnancy in 2015-2016. We evaluated the women who subsequently developed PIH (n = 137) (gestational hypertension-GH (n = 113) and pre-eclampsia-PE (n = 24)), and the women who remained normotensive (n = 775). The diseases odds ratios (and 95% CI-confidence intervals) were calculated in a multivariate logistic regression. In the PIH cases (vs. normotensive women) we found more smokers (25.6% vs 17.2%, p = 0.020) including smokers in the first trimester (14.6% vs 4.8%, p <0.001). The average number of cigarettes smoked daily per smokers in the first trimester was 11.2 (range 2-30), and the average number of years of smoking was 11.6 (range 2-25). The number of years of smoking was a stronger risk factor for GH and PE than the number of cigarettes/day. Compared to the women who have never smoked, smoking ever before pregnancy was associated with a higher GH risk (AOR = 1.68; p = 0.043), and with no effect on PE risk (OR = 0.97; p = 0.950). Smokers in the first trimester had a higher odds ratio of GH (AOR = 4.75; p <0.001) and PE (OR = 2.60; p = 0.136). Quitting smoking before pregnancy (ex-smokers) was associated with a lower odds ratio of GH (AOR = 0.83; p = 0.596) and PE (OR = 0.33; p = 0.288). However, quitting smoking during pregnancy was associated with a higher risk of GH (AOR = 11.63; p <0.0001) and PE (OR = 3.57; p = 0.238). After dissection of the cohort into pre-pregnancy body-mass index (BMI) categories, smoking in the first trimester was associated with the higher hypertension risk in underweight women (OR = 22.00, p = 0.024). Conclusions: The factors that increased the risk of GH and PE were smoking in the first trimester and (paradoxically and more strongly) smoking cessation during pregnancy. Our results suggest that women of childbearing potential should be encouraged to quit smoking before pregnancy.
Keywords: gestational hypertension; pre-eclampsia; pregnancy; smoking; smoking cessation; underweight.