Ultrasound is a commonly performed test in obstetrics. Numerous studies have confirmed that ultrasound during pregnancy is safe and does not cause adverse effects on the fetus. Prolonged, high-dose, high-frequency ultrasound irradiation can cause the phenomenon of cavitation of the gestational sac, but this situation is generally only found in animal model experiments, the ultrasound used in clinical practice is not so, do not have to worry. MRI (magnetic resonance imaging), like ultrasound, is not radioactive and does not produce ionizing radiation. A few animal fetal studies have found that exposure to the magnetic field of MRI in early pregnancy may be teratogenic, but some animal studies have not found any effect, and there is no information on human studies yet. “However, the 2007 U.S. Radiation Safety Guidelines state that MRI can be performed at any stage of pregnancy as long as the patient is comfortable with the risks and benefits of MRI, while the latest U.S. Food and Drug Administration (FDA) guidelines require that MRI instruments should be labeled with the statement that the fetal examination “has not yet been established for safety evaluation. “. In clinical practice, the majority of cases of MRI examination is pregnant women have other diseases, need to further identify the condition and treatment, and ultrasound and other routine examination and failed to confirm the diagnosis, at present, it is generally believed that MRI examination in late pregnancy is relatively safe, after assessing the advantages and disadvantages of a variety of conditions can be selected according to the needs of the disease, should be avoided as far as possible to do MRI in the early stages of pregnancy.