Hare lip, also known as cleft lip, is one of the common facial deformities caused by teratogenic factors that cause the medial nasal and maxillary processes to fail to fuse on one side during embryonic development, which in turn leads to unilateral or bilateral cleft lip. Cleft lip can affect facial development, articulation and swallowing. The causes of cleft lip mainly include genetic factors and viral infections, etc. 1. Genetic factors: If someone in the family has suffered from harelip, the probability of the offspring suffering from harelip is relatively high, and the closer the relatives are, the higher the prevalence rate will be, with genetic factors accounting for about 78%; 2. Other factors: Pregnant women who smoke, drink alcohol, take anti-epileptic drugs, antiemetic drugs, are exposed to pesticides, radiation or toxic chemicals, or have vitamin deficiency during pregnancy, diabetes, gynecological diseases, abnormal thyroid function, or elevated levels of alpha-fetoprotein can increase the risk of cleft lip. Therefore, in order to prevent the occurrence of cleft lip, regular maternity checkups should be performed during pregnancy, with ultrasound being preferred for screening. Ultrasound is an important tool to diagnose cleft lip deformity, which has the advantages of visualization, safety, reproducibility, and high diagnostic rate to achieve eugenics as much as possible.