Inclusion Criteria:Part I: Evaluation of the efficacy of aspirin in preventing preeclampsia and severe pregnancy complications 1.11-13 + 6 gestational weeks; 2.≥18 years old; 3. Monocyesis, fetal survival; 4. Agree to participate and sign the informed consent. Part II: The establishment of a risk prediction model for severe pregnancy complications of hypertensive disorders of pregnancy 1.20-36 + 6 gestational weeks 2. Diagnosed ≥1 of the following diseases ① Hypertension during pregnancy ② Preeclampsia ③ Pregnancy complicated with chronic hypertension ④ Chronic hypertension with preeclampsia 3.≥18 years old; 4. Monocyesis, fetal survival; 5. Agree to participate and sign the informed consent.  -  Exclusion Criteria:Part I: Evaluation of the efficacy of aspirin in preventing preeclampsia and severe pregnancy complications 1. Twin or multiple pregnancies; 2. Severe fetal malformation/abnormality; 3. Routine aspirin use before enrollment; 4. Have a history of aspirin contraindications, such as salicylic acid allergy, ulcerative disease of the digestive tract, and bleeding, liver cirrhosis, kidney failure, platelet count < 50 x 109 / L, hematocrit < 10%, hemophilia, congenital platelet disease, fibrinogen defects, or shortage, taking other antiplatelet agents except for aspirin, the use of anti-inflammatory drugs or the use of warfarin. 5. Patients who have been diagnosed with hypertensive disorders of pregnancy; 6. Severe mental disorder and inability to express will; 7. If she has obvious other abnormal physical signs, laboratory tests, and other clinical diseases, she is not suitable to participate in the study as judged by the researcher; 8. According to the researcher's judgment, childbirth information could not be obtained through observation and follow-up. Part II: The establishment of a risk prediction model for severe pregnancy complications of hypertensive disorders of pregnancy 1. Twin or multiple pregnancies; 2. Severe fetal malformation/abnormality; 3.Severe mental disorder and inability to express will; 4.If she has obvious other abnormal physical signs, laboratory tests, and other clinical diseases, she is not suitable to participate in the study as judged by the researcher; 5. According to the researcher's judgment, childbirth information could not be obtained through observation and follow-up.  -