At present, ultrasound examination of pregnant women is already a common routine examination, but many friends do not know much about the safety of ultrasound examination and the precautions of ultrasound examination during pregnancy, so we will do a brief discussion on these issues. Ultrasound is a high-frequency acoustic signal that is beyond the upper limit of the human hearing range, generally with a frequency greater than 20,000 Hz. In 1880, Madame Curie’s husband Pierre and brother Jacques discovered together to some crystals pressurized, it will produce electric charge; then in turn to these crystals a certain amount of alternating voltage, it will produce mechanical waves, with the voltage of the Hertz becomes larger mechanical wave frequency also becomes larger, thus producing ultrasound. The real application of ultrasound to the field of medical diagnosis was in the 1940s and 1950s, after the efforts of Austrian, German and American scientists, ultrasound diagnostic instruments were finally put into use. In the past half century or so, ultrasound has gradually become the most common examination method. Compared with X-ray examination, it has almost no side effects; compared with MRI, it is more inexpensive. In the late 1950s, ultrasound was used in obstetrics. Ultrasound is currently the safest and most effective method of obstetrical examination. During pregnancy, a pregnant woman typically undergoes several ultrasound examinations. In order to optimize the collection of information, ultrasound examinations are performed in well-defined time periods. Generally, the first ultrasound is performed in the 18th – 20th week. It provides a general diagnosis of fetal malformations and observes the state of fetal activity. The purpose of the second ultrasound in the 34th week of pregnancy is to monitor the amount of amniotic fluid, the position of the placenta, the maturity of the placenta and the presence of fetal anomalies, and to know whether the fetal development corresponds to the gestational week. Finally, after the 37th week, the main purpose of the ultrasound examination is to determine the mode of delivery and to monitor the amount of amniotic fluid, placental maturity and, if necessary, the need for weekly ultrasound. Of course, this is only the most routine examination. If a pregnant woman has vaginal bleeding or sudden abdominal pain in early pregnancy, she can use ultrasound to determine if the fetus is alive and if there is any abnormal pregnancy. Secondly, if the pregnant woman suffers from other diseases affecting pregnancy such as diabetes and hypertension, the number of ultrasound examinations should be increased. At the moment we say that ultrasound is not 100% reliable. It is not a diagnostic test, but only a screening test. For certain organs that are not functioning well, ultrasound is not able to detect them. Also, it is limited and interfered by many factors as far as the accuracy of its examination is concerned. Currently, ultrasound can generally screen out 70% to 80% of congenital abnormalities. The success rate of screening can vary somewhat for different developmental abnormalities. In summary, it is safe and reliable for pregnant women to undergo necessary ultrasound examinations during pregnancy. Ultrasound itself is also meaningful in detecting fetal malformation rates. However, it does not mean that meaningless ultrasound examinations can be performed freely during pregnancy. When to check, what part of the body to check, and what kind of examination method to use will be different for different pregnant women. We still need to strictly follow the clinician’s recommendations and perform the formal and necessary ultrasound examinations.