When to do ultrasound needs to be judged according to the specific examination items, usually abdominal ultrasound examination in the morning in the fasting state, heart, vascular parts of the ultrasound examination is generally not subject to time restrictions, the uterus, pelvic ultrasound examination is recommended after the end of the physiological period, and pregnancy ultrasound needs to be based on the specific needs of the examination: 1, abdominal ultrasound: liver, bile, pancreas, spleen, kidney and other abdominal organs examination in fasting The examinee should not eat or drink 8 hours before the examination to avoid accumulation of water and gas in the gastrointestinal tract, which will interfere with the examination results, and eating will also affect the state of bile evacuation and affect the morphological observation of the gallbladder; 2. Ultrasound: Ultrasound of the urinary system often needs to be performed with a full bladder, and the examination can be preceded by drinking water; pelvic ultrasound of the uterus and its adnexa is recommended to be performed after the end of the physiological period, while breast examination is recommended to be performed 3-7 days after the end of the physiological period to avoid changes in estrogen levels affecting glandular morphology, etc.; 4. Ultrasound during pregnancy: Pregnancy care guidelines recommend at least eight maternity examinations during pregnancy, of which several times need to be performed Ultrasound examinations are needed several times to observe the fetal development at any time, and the time of maternity examinations includes 6-13 weeks, 20-24 weeks, etc. If there are suspicious abnormal manifestations, the number of ultrasound examinations can be increased as appropriate.