Paternity testing is the use of genetics, medicine, physiology and other theories and techniques to determine whether a child and its parents are related by the similar characteristics of the physical skills and morphological structures of the offspring and the parent. In general, DNA is used to determine, and human blood, saliva, hair, etc. can be used for paternity testing. What is needed for paternity testing during pregnancy is DNA identification. DNA is already present when the egg cells and sperm unite to form a fertilized egg. There are a large number of shed embryonic tissue cells in the mother’s amniotic fluid, and amniotic fluid sampling can be used for paternity testing, but it is generally recommended that amniocentesis be performed between 16 and 24 weeks of pregnancy for paternity testing. For earlier identification, a chorionic villus biopsy can be done between 10 and 13 weeks of pregnancy, but this technique is not available in all cities and can only be done in cities with high medical standards, such as Beijing and Shanghai. Although paternity testing during pregnancy does not have a significant impact on the fetus, it is important to choose a regular and authoritative hospital. The paternity test is ethically harmful to the child and is not conducive to the child’s growth, so try not to do paternity testing unless you have to do it under special circumstances to avoid unnecessary harm.