Objective To explore the clinical characteristics and pregnancy outcomes of twin pregnancies complicated with severe preeclampsia.Methods The pregnant outcomes of 131 twin pregnancies (twin group) and 572 singleton pregnancies (singleton group),all complicated with severe preeclampsia,were analyzed retrospectively.All patients were treated in the Department of Obstetrics and Gynecology,West China Second University Hospital,Sichuan University from June 2007 to June 2011.The patients' age,onset of disease,gestational weeks at delivery,mean duration of expectant treatment,blood pressure,laboratory parameters and incidence of pregnancy complications,including placental abruption,heart failure,pulmonary edema,postpartum hemorrhage,uteroplacental apoplexy,eclampsia,HELLP syndrome (hemolysis,elevated liver enzymes and low platelets syndrome),hypoproteinemia,retinopathy,intracranial hemorrhage and renal insufficiency,were compared between the two groups.Perinatal outcomes such as premature delivery,perinatal mortality,neonatal intensive care unit (NICU) hospitalization,fetal distress,hypoxic-ischemic encephalopathy (HIE),asphyxia neonatorum,neonatal pneumonia,hyperbilirubinemia and neonatal hypoglycemia of two groups were also compared.Chi-square test,Fisher's exact test or t-test were used for statistical analysis.Results The severe preeclampsia incidence of twin pregnancies (5.03％,131/2604) was higher than that (1.94％,572/29 452) of singleton pregnancy (x2=106.40,P＜0.001).The onset time [(33.6±1.8) weeks] and gestations at delivery [(34.6±2.9) weeks] in twin group were earlier than those in singleton group [(34.4± 2.0) weeks,t=2.364,P＜0.05; (35.6±3.2) weeks,t=3.902,P＜0.05].The duration of expectant treatment of twin group [(6.4±0.3) d] were shorter than that of singleton group [(7.4± 0.5) d,t=5.314,P＜0.01].The incidence of placental abruption [9.9％ (13/131) vs 4.2％ (24/572),x2=7.013,P＜0.01],heart failure [11.5％ (15/131) vs 3.2％ (18/572),x2=16.430,P＜0.01],pulmonary edema [4.6％ (6/131) vs 0.9％ (5/572),x2=9.505,P＜0.01],postpartum hemorrhage [16.0％ (21/131) vs 7.0％ (40/572),x2 =10.990,P ＜ 0.01] and uteroplacental apoplexy [5.3％ (7/131) vs 0.5％ (3/572),x2 =17.650,P＜0.01] of twin group were higher than those of singleton group,respectively.The incidence of premature delivery [77.1％ (202/262) vs 29.9％ (171/572),x2=162.000,P＜0.05],NICU hospitalization [76.2％ (205/262) vs 58.4％(332/572),x2 =31.980,P＜0.05] and HIE [8.4％ (22/262) vs 4.7％ (27/572),x2 =4.392,P＜0.05] of twin group were higher than those of singleton group,respectively.Conclusions Twin pregnancy women are more likely to be complicated with severe preeclampsia and more vulnerable to suffer from severe complications,resulting in poor perinatal outcomes.More attentions should be paid on the management of twin pregnancy.Once hypertensive disorders complicating pregnancy is diagnosed,active management should be provided and timing of termination should be considered.