The effect of smoking on pre‐eclampsia in twin pregnancy

OBJECTIVE: To assess the effect of smoking on the incidence of pre-eclampsia and on perinatal outcome in twin pregnancy. DESIGN: Retrospective study using Aberdeen Maternity and Neonatal Databank. SETTING: Grampian, Orkney and Shetland. POPULATION: All 1,575 twin pregnancies delivered in the years 1969-1971 and 1976-1997 (when smoking data were available). METHODS: In all twin pregnancies the effects of smoking on pre-eclampsia were analysed by parity and gestation at delivery. The effect of smoking upon late miscarriage and perinatal outcome was analysed without subdivision. MAIN OUTCOME MEASURES: Pre-eclampsia and perinatal outcome. RESULTS: Primiparae had significantly higher rates of pre-eclampsia than multiparae and were delivered significantly earlier. The incidence of pre-eclampsia in smokers was significantly lower only in multiparae. Length of gestation was significantly shorter in multiparous smokers. The effect of smoking on pre-eclampsia appeared to be direct in multiparae but possibly indirect in primiparae (by causing earlier delivery). Smokers had a higher late miscarriage rate than nonsmokers. CONCLUSIONS: In twin pregnancy the apparent protective effect of smoking against pre-eclampsia is significant only in multiparae, suggesting that in primiparae the smoking effect is overwhelmed by the other reasons for the development of pre-eclampsia. Smoking in twin pregnancy is not recommended due to the worse fetal outcome rates.