Although ultrasonography is currently the most effective method to screen for fetal structural malformations, there are a wide variety of fetal malformations and a significant number of malformations that are undetectable or unrecognizable by ultrasound. In particular, ultrasound diagnosis of some birth defects without obvious morphological changes is still difficult and cannot replace all prenatal diagnostic techniques. A normal ultrasound examination also does not guarantee an absolutely normal fetal pregnancy outcome. Clinicians and pregnant women should be aware of the purpose, detection rate and limitations of ultrasonography during pregnancy. Expert consensus: Currently it is unrealistic and unreasonable to expect that all fetal anomalies can be detected, regardless of the method used, even if the most renowned specialists are allowed to perform a thorough examination. With the application of MRI in obstetrics, it has obvious advantages in the diagnosis of fetal neural tube abnormalities, especially in large gestational weeks (more than 30 weeks), when ultrasound observation is difficult, it can make up for the shortcomings of ultrasound, and with the continuous improvement of MRI technology, it can be a good complement to ultrasound, helping ultrasound to “check the gaps”. With the continuous improvement of MRI technology, it can be a good supplement to ultrasound and help ultrasound to “check for gaps”. What are the risks of prenatal ultrasound examination? 1.Anomalies that are easily missed by prenatal ultrasound: polydactyly, syndactyly, missing toes, microtia, missing ear, ear position change, small ventricular septal defect, coronary artery anomaly, ectopic drainage of pulmonary veins, lower gastrointestinal atresia (anal atresia), etc. 2. Diseases that cannot be diagnosed by ultrasound: foramen ovale noncompaction, atrial septal defect type II, ductus arteriosus noncompaction, mental retardation, hearing impairment, visual impairment, cerebral palsy, metabolic diseases, genetic diseases, etc.