Moderate smoking during pregnancy is associated with a reduced risk of preeclampsia

Background. To investigate the effects of maternal smoking during pregnancy on the development of preeclampsia (PE). Methods. The study comprised two populations with singleton pregnancies, on e collected from 1990 to 1994 at the Malmo University Hospital (Malmo serie s, n=14,510) and the other from the National Birth Registry of Sweden 1993 (National series, n=113,211). Women with PE (n=281 and n=2,865, respectivel y) were compared to those without PE, delivered in 1993 (n=2,811 and n=110, 346, respectively). The subgroups of women who had PE associated with prete rm birth (n=58 and n=693, respectively) were compared with the same control groups in both series. Results. Multiple logistic regression analysis showed that, in comparison w ith non-smokers, moderate smokers (1-9 cigarettes per day) were characteriz ed by a lower incidence of PE (odds ratio (OR) 0.4; 95% confidence interval (CI) 0.22-0.60), and PE associated with preterm birth (OR 0.1, 95% CI 0.01- 0.67). The corresponding figures in the validating National series were als o significantly lower for moderate smokers (OR 0.6; 95% CI 0.5-0.7 and OR 0 .6; 95% CI 0.5-0.8, respectively). Conclusion. Moderate smoking during pregnancy seems to protect against the development of PE and PE associated with preterm birth. Nicotine might be t he agent responsible for this protective effect.