Pregnancy with a harelip usually has no precursor and is usually diagnosed by ultrasound during a maternity checkup. A cleft lip is a congenital abnormality that occurs in the early embryonic period when the embryonic lobe tissue in the lip position in the fetus’s oral cavity is obstructed. The normal development of the fetus’s maxillofacial position is interfered with by a variety of reasons, which results in a cleft lip abnormality in the fetus, and the causes of the abnormality in the fetus include both genetic factors and environmental factors. If a pregnant woman has an immediate or collateral family member with cleft lip, the condition may be inherited during pregnancy. A cleft lip can also be caused by cytomegalovirus and murine rubella virus. The symptoms of cleft lip can also be caused by deficiencies in vitamin A, magnesium and nutrients such as pantothenic acid and riboflavin. Therefore, it is recommended that women go to the hospital for a comprehensive examination before pregnancy to avoid the phenomenon of cleft lip. During pregnancy, it is also necessary to undergo regular obstetric examination to detect fetal malformations through ultrasound, and choose whether to continue the pregnancy according to the individual’s situation. During pregnancy, pregnant women should pay more attention to diet and ensure balanced nutrition.