The first ultrasound examination is usually performed around 40 days of pregnancy. Ultrasound is a non-invasive test, and the ultrasound equipment and coupling agent are harmless to the fetal growth and development; vaginal ultrasound or transabdominal ultrasound can be done during early pregnancy, and transabdominal ultrasound is the main test in the middle and late pregnancy. The ultrasound can determine the size of the gestational sac and the exact duration of the pregnancy. This is the most important significance of ultrasound in the early stage. Normally, around 35-40 days, a dark area can be seen in the uterine cavity, and after 40 days, yolk sac, germ, and primitive fetal heartbeat gradually appear, so it is better to have the first ultrasound examination at this time. 20-24 weeks and 28-32 weeks, respectively, two 4D ultrasounds are needed to systematically understand the fetal development and screen for fetal malformations. In addition, when you have your first ultrasound examination, you can drink a lot of water before the examination and hold your urine in advance to make your bladder full, so that the ultrasound phenomenon will be clearer and easier for the doctor to observe the intrauterine situation.