Tobacco use during pregnancy and preeclampsia risk: effects of cigarette smoking and snuff.

Preeclampsia is a leading cause of maternal and infant mortality and morbidity worldwide. Both Swedish snuff and cigarette smoke include nicotine, but combustion products accompany only smoking. The aims of this study were to compare the effects of Swedish snuff and cigarette smoking on preeclampsia risk and to estimate whether changes in tobacco habits during pregnancy affect the risk of developing term preeclampsia. We used information from the Swedish Birth Register on all singleton births in Sweden during the years 1999-2006 (n=612 712). Compared with nontobacco users, women who used snuff in early pregnancy had an adjusted odds ratio (OR) for preeclampsia of 1.11 (95% CI: 0.97 to 1.28). The corresponding ORs for light and heavy smokers were 0.66 (95% CI: 0.61 to 0.71) and 0.51 (95% CI: 0.44 to 0.58), respectively, with ORs lower for term than preterm preeclampsia. Compared with nontobacco users, women who smoked in early pregnancy but had quit smoking before late pregnancy (weeks 30 to 32) had an adjusted OR for term preeclampsia of 0.94 (95% CI: 0.83 to 1.08). The corresponding OR for women who did not use tobacco in early pregnancy but had started to smoke before late pregnancy was 0.65 (95% CI: 0.50 to 0.85). We conclude that tobacco combustion products rather than nicotine are the probable protective ingredients against preeclampsia in cigarette smoke. Because change of smoking habits during pregnancy influence risk, we further conclude that it is the smoking habits in the middle or late rather than in the beginning of pregnancy that seem to affect the risk of preeclampsia.