2D ultrasound is general ultrasound, which is a commonly used non-invasive examination method. The specific time to do 2D ultrasound needs to be decided according to the purpose and parts of the examination, and cannot be generalized. 2D ultrasound can generally be used as an auxiliary examination in departments such as surgery, gynecology and obstetrics: i. Surgery: If it is the circulatory system, such as checking the heart and brain vessels, when to do ultrasound can be done, and it is not affected by eating or time. If it is the digestive system, such as examination of the liver, gallbladder, spleen, stomach, etc., the examination should be done after 8 hours of fasting, so that the size, shape and internal structure of the organs can be observed. Second, gynecology: uterus, ovaries, fallopian tubes, etc. should be examined after holding urine, which can check whether there are abnormal masses or cysts in the uterine attachments. Obstetrics: 1. Determine the location of the gestational sac: you can go to the hospital at 6-7 weeks of pregnancy to confirm the location of the gestational sac through ultrasound examination to exclude the possibility of ectopic pregnancy; 2. It can guide the choice of delivery method. In addition, 2D ultrasound can also observe the direction and function of gallbladder, bile duct, bladder and ureter, etc. The best examination time can be chosen under the guidance of doctors, which is conducive to improving the accuracy of examination and thus early detection of abnormalities for treatment.