The Effectiveness of Aspirin on Preventing Pre-eclampsia

Inclusion Criteria: * Age between 18-55 years * Gestational age between 12-20 weeks of pregnancy * High risk of developing pre-eclampsia * At least one of the following risk factors: Pre-eclampsia in a previous pregnancy , Multiple pregnancy，Diabetes Mellitus(Type 1 or 2), Chronic Hypertension，Renal disease, Autoimmune disease. * At least two of the following risk factors: Primiparity，Pre-pregnancy Body Mass Index ≥28kg/m2, Age ≥35 years, Family members have a history of pre-eclampsia. * Maternal informed conset obtained Exclusion Criteria: * Contraindication to aspirin therapy (including but not limited to allergy and high bleeding risk) * Patient with known intention to terminate pregnancy * Fetal abnormalities detected （including but not limited to major fetal malformation and FGR） * Severe heart, liver, renal disease who can not burden the experiment * Alcohol and drug abuse * Being in another drug experiment within 3 months