Close relatives are usually defined as having a common ancestor for three generations or less. Close relatives are not allowed to stay together, and consanguineous marriages largely increase the probability of fetal malformations and polygenic genetic diseases. As close relatives acquire more identical genes from a common ancestor, it is easy for recessive genes unfavorable for survival to meet in the offspring, thus making it easy to produce children of inferior quality. The offspring of consanguineous marriages have a higher incidence of polygenic and recessive genetic diseases, such as congenital heart disease, anencephaly, schizophrenia and other diseases. In addition, there is a higher incidence of early deaths, fetal malformations, and dementia in offspring of consanguineous marriages compared to offspring of non-consanguineous marriages. Therefore, direct blood relatives and collateral blood relatives within three generations can not be together, it is recommended that is not the above mentioned close relatives, should promptly seek medical attention, under the guidance of the doctor, improve the relevant examination, to clarify whether they can be together.