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 1575 twin pregnancies delivered in the years 1969-1971 and 1 976-1997 (when smoking data were available). Methods In all twin pregnancies the effects of smoking on pre-eclampsia wer e 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 mul tiparae and were delivered significantly earlier. The incidence of pre-ecla mpsia in smokers was significantly lower only in multiparae. Length of gest ation was significantly shorter in multiparous smokers. The effect of smoki ng on pre-eclampsia appeared to be direct in multiparae but possibly indire ct in primiparae (by causing earlier delivery). Smokers had a higher late m iscarriage rate than nonsmokers. Conclusions In twin pregnancy the apparent protective effect of smoking aga inst pre-eclampsia is significant only in multiparae, suggesting that in pr imiparae the smoking effect is overwhelmed by the other reasons for the dev elopment of pre-eclampsia. Smoking in twin pregnancy is not recommended due to the worse fetal outcome rates.