Congenital defect refers to the developmental disorder that has been formed before the baby is born, including congenital malformation with abnormal morphological structure and metabolic function and congenital mental retardation. Because all kinds of developmental disorders occur before birth, they are called congenital defects. There are many kinds of congenital defects, but they can be divided into four types. 1. Congenital defect of morphological structure, showing congenital malformation. There are hundreds of morphological and structural defects, such as surface and visible deformities, as well as internal organ and tissue deformities. 2. Congenital defects caused by physiological and metabolic dysfunction. It is characterized by dysfunction, such as congenital deafness's disease, deafness and blindness, and metabolic abnormality, such as phenylketonuria. 3. Congenital mental retardation includes mental retardation caused by various chromosome aberrations, mental retardation caused by monogenic diseases and polygenic genetic diseases, and mental retardation caused by environmental teratogenic factors, such as alcoholism syndrome, Minamata disease, lead poisoning, congenital rubella syndrome and mental retardation caused by environmental iodine deficiency affecting fetal brain development. Some newborn babies' mental retardation is not easy to be found, and it doesn't begin to show until about 3 years old, and it can only be confirmed by examination when they are older. 4. Fetal intrauterine growth retardation. Although most children with intrauterine growth retardation gain weight quickly after birth, their intelligence development is poor and their IQ is low, so they are also congenital defects.