Abstract： Objective To identify the early warning signs of severe preeclampsia (SPE). Methods A case-control (1: 2) observational study was conducted. Forty-seven pregnant women with SPE, who attended the prenatal clinics of Peking University Third Hospital regularly from Jan. 2002 to Dec. 2007, were selected as the study group, including 12 early onset and 35 late onset ones. The control group consisted of 94 healthy singleton pregnant women at the same period. Clinical data were collected and analyzed. Results (1) The basal body mass index (BMI) showed no difference between the study and control group [(23.27±4.31)kg/m2 vs (21.52±3.09)kg/m2, P>0.05]. (2) The net increase of BMI in the study group before the onset of SPE was higher than that in the control [(5.60±2.17)kg/m2 vs (4.85±1.52)kg/m2, P<0.05] and the increase of BMI per week was also higher [(0.74±0.41)kg/(m2*w)-1 vs (0.23±0.18)kg/(m2*w)-1, P<0.01]. The sensitivity and specificity of BMI increase per week in predicting SPE was 84% and 81% at a cut-off value of 0.39 kg/(m2*w)-1, respectively, and 79% and 91% at 0.41 kg/(m2*w)-1 correspondingly. (3) During the third trimester and before the onset of SPE, the weight gain per week in the study group was higher than that of the control [(0.93±0.70)kg vs (0.63±0.20)kg, P<0.01]. Significant difference was also found in the net weight gain between the two groups (P<0.01), but not in the percentage of women with excessive weight gain (>0.50 kg/w) [60%(25/42) in the study group vs 63%(53/84) in the control group, P>0.05]. (4) Higher percentage of women experienced pre-hypertension in the study group than in the controls [17%(8/47) vs 5%(5/94), P<0.01]. (5) In the study group, 53%(25/47) of the women had edema before SPE onset, but the figure dropped to 18% (17/94) in the controls(P<0.01). (6) Eight women in the study group and one in the control group suffered from hypoproteinemia before SPE onset with the average level of plasma albumin of (32.6±1.6)g/L and(38.4±2.1)g/L(P<0.01), respectively. (7) Proteinuria was reported in 10 cases (21%)in the study group and 4(4%) in the controls (P<0.01). (8) Logistic regression analysis showed that the risk factors for SPE included edema (OR=6.16,95%CI:2.29-16.57),pre-hypertension (OR=6.21,95%CI:1.56-24.77),proteinuria (OR=9.68,95%CI:1.86-50.30), and weight gain >0.85 kg/w during the third trimester (OR=11.60,95%CI:3.54-37.97). Conclusions Edema, excessive weight gain,pre-hypertension and hypoproteinemia are early warning signs of SPE. Pregnant women with the above signs required close monitoring during prenatal care.