Recently, pregnant women and their families often ask if they can have an ultrasound after pregnancy. In my clinic, there are often cases where pregnant women are asked to have an ultrasound and are refused. The reason is that ultrasound is harmful to the fetus. I would like to discuss the importance and necessity of B-ultrasound in different periods of pregnancy based on relevant information and my personal experience. In addition to the urine hCG test, if the menopause is longer than 40 days, an ultrasound should be performed. The importance of this test is: 1. To confirm whether you are pregnant or not. 2. 2. To confirm the location of the pregnancy, whether it is intrauterine or ectopic. 3. In case of intrauterine pregnancy, the development of the germ and the presence of primordial ventricular pulsations should be understood. 4.Identify pathological pregnancy, such as gravidity, etc. As can be seen above, ultrasound is necessary in the early stages of pregnancy. II. Mid-pregnancy The mid-pregnancy is an important stage of individual fetal development, so ultrasound should be performed every 3-4 weeks, mainly to closely understand the development of the fetus, and to detect some large fetal malformations at an early stage. The main purpose of the ultrasound is to closely monitor the development of the fetus and to detect any major abnormalities in the fetus. In late pregnancy, the fetus is about to be delivered from the mother, so how big is the fetus after full term? Can the baby be delivered vaginally? What is the condition of the placenta? What is the position of the placenta? Is the umbilical cord tangled? Ultrasound can be used to help diagnose these problems. Thus, it is very important and necessary to perform ultrasound examinations at different stages of pregnancy.