Ultrasound is a B-mode ultrasound examination, which is one of the more used and widely used clinical examination methods. It is a method that uses high-frequency sound waves to image the internal tissues and organs of the body in a brightness pattern in order to facilitate the observation of tissue morphology. Ultrasound is a relatively safe test because it does not cause any adverse effects on the fetus, unlike X-rays, CT or MRI, and is not associated with ionizing radiation. However, ultrasound examinations should not be performed more than 6 times during the whole pregnancy, otherwise it will have certain effects on the fetus, except for special cases such as doctor’s request. Ultrasound examination is relatively safe and women often have to do the corresponding examination through ultrasound after pregnancy. Currently, color ultrasound is used to observe the fetus in the middle of pregnancy, to assess its growth and development and to check whether there is any fetal malformation. There are no reports of fetal malformations caused by multiple ultrasounds during pregnancy, and there is no laboratory evidence, so it is generally believed that ultrasound examinations do not have any adverse effects on the fetus, and a coupling agent is applied to the body during ultrasound examinations, mainly to couple the probe of the ultrasound instrument and improve the clarity of the display. The coupling agent is mainly sodium alginate, sodium carboxymethyl cellulose or carbomer with water, glycerin or propylene glycol, which are harmless substances that moisturize the skin and will not harm the fetus in the uterine cavity through the skin. Both the sound waves of the ultrasound examination instrument and the coupling agent used during the examination are harmless to the body, not to mention harming the fetus, and are safe examination methods. However, it is not possible to have frequent examinations because of its relative safety. Generally, you need to have ultrasound 3 times during pregnancy, not more than 6 times, but if the pregnant woman has some abnormalities, or the doctor will ask for more times in order to check certain conditions, you need to follow the doctor’s advice in these cases.