Four-dimensional color ultrasound to the fetus to do macroanomaly examination although the accuracy rate is relatively high, but there is also a certain leakage rate, so four-dimensional may not be able to find small jaw malformation. Although 4D ultrasound is the most comprehensive three-level prenatal systematic screening for fetal malformations, it can’t completely screen out all fetal malformations, and has certain limitations, so it is possible to miss the diagnosis of small jaw malformations. Fetuses with micrognathia are often associated with other developmental anomalies, such as pulmonary hypertension, atrial septal defects, arterial stenosis, etc., and some of these anomalies may also affect mental development. If micrognathia is detected by 4D ultrasound, systematic examination of other organs should be conducted in detail, and amniocentesis should be performed to determine whether there is any chromosomal disease, and if necessary, terminate the pregnancy according to the doctor’s advice.