Abstract： Objective:To analyze the clinical features and pregnancy outcomes in antepartum and postpartum hemolysis, elevated live enzymes, and low platelet count syndrome(HELLP syndrome).Methods:A retrospective study was conducted to collect maternal and neonatal information of pre-eclampsia complicated with HELLP syndrome in Peking University First Hospital during the ten years from April 2009 to March 2019. A total of 83 pregnant women were included according to the Tennessee Classification System. They were then allocated into two groups based on the onset time of HELLP syndrome: antepartum HELLP syndrome group ( n=70) and postpartum HELLP syndrome group ( n=13). The clinical features, symptoms, laboratory biomarkers, and pregnancy outcomes were compared between the two groups. Results:Among the 83 pregnant women with HELLP syndrome, 70 occurred prenatally (84%, 70/83) and 13 occurred postpartum (16%, 13/83). The twin or triplet pregnancy rate in the postpartum HELLP syndrome group was significantly higher than that in the antepartum HELLP syndrome group [6/13 vs 6% (4/70), P=0.001]. The gestational weeks for HELLP onset and delivery in the postpartum HELLP syndrome group were significantly later than those in the antepartum HELLP syndrome group [(35.8±3.0) vs (31.5±5.2) weeks, P=0.025; (36.7±2.3) vs (32.2±5.0) weeks, P=0.002]. The incidence of early-onset pre-eclampsia in the antepartum HELLP syndrome group was significant higher than that in the postpartum HELLP syndrome group [64% (45/70) vs 2/13, P=0.002]. The quantitative of 24-hour proteinuria was significant higher in the antepartum HELLP syndrome group than that in the postpartum HELLP syndrome group [(4.8±5.1) vs (1.8±1.6) g, P=0.002]. But there were no statistical significances in the comparison of other laboratory test indexes (all P>0.05). There were no significant differences between the two groups in clinical symptoms, severe maternal complications, transfusion or adverse maternal outcomes (all P>0.05). Conclusions:Antepartum and postpartum HELLP syndrome have similar clinical symptoms and laboratory characteristics. Both antepartum and postpartum HELLP syndrome could lead to severe maternal complications, which should be paid special attention in clinical practice, especially to the postpartum HELLP syndrome.