The harelip is a relatively common clinical phenomenon of fetal developmental malformation, pregnant women in pregnancy after the fetus harelip, may be due to the following factors: 1, may be pregnant women exposed to harmful substances to the body caused by exposure to radiation, X-ray or formaldehyde, toluene, etc., may lead to fetal developmental deformities; 2, may be due to genetic factors, if 2, may be caused by genetic factors, if there are harelip in the immediate family, the children will have a higher chance of harelip, is due to chromosomal abnormalities caused by the phenomenon of harelip; 3, with the drugs taken during pregnancy has a relationship, if you take sleeping pills or cold medicine during pregnancy, may lead to the occurrence of the harelip of the fetus; 4, it may be in the period of pregnancy, the uterus cavity viral infections caused by, such as rubella virus.