The fetus is prone to malformations in the first 3 months of pregnancy, and most of the major malformations can be screened for in the middle of pregnancy (18-22 weeks). During the 12th week of pregnancy, the fetus is at a critical stage of development and is prone to malformations because it is the stage of differentiation and development of various tissues and organs of the fetus and the nervous system. If the pregnant woman is exposed to chemical substances, radioactive substances and undesirable drugs at this time, it may lead to fetal developmental malformations. In addition, abnormal development of the fertilized egg, viral infection, karyotype abnormalities and genetic mutations are also key causes of fetal developmental malformations. After the 12th week of pregnancy, the fetal organ systems are already formed, and adverse chemicals or drugs have less effect on the fetus. Usually, the major fetal malformations can be screened out in 18-22 weeks of pregnancy. Pregnant women are advised to pay attention to rest in early pregnancy, avoid straining and catching cold, not to take medication without permission and avoid exposure to undesirable substances. At the same time, pay attention to supplementing eggs, milk, chicken, fish and other high quality proteins, as well as increasing the intake of fresh vegetables and fruits and carbohydrates.