Sex identification refers to the application of medical, biological and genetic theories, polymerase chain reaction technology, fluorescence quantitative analysis technology and so on. To determine the sex of the fetus, DNA chromosomes were separated by centrifugation for many times, and whether Y chromosomes existed in blood samples was detected. Sex identification is usually to take 12ml of pregnant women's blood before the birth of the fetus, and detect and analyze the fetal DNA chromosomes dissociated from the mother to identify the sex of the fetus. Pregnant women can know the sex of the fetus through DNA sex identification as early as 7 weeks after pregnancy, and the accuracy rate can reach 99.4%. Sex identification is prohibited in China, so Dalian can't do sex identification of DNA chromosomes.

Clinical application of fetal Y-DNA detection: The procedure of fetal Y-DNA (male DNA) detection is to identify whether there is Y chromosome DNA in pregnant women's blood during pregnancy. The results of many clinical studies have proved that Y-DNA can be reliably detected in pregnant women in the eighth week of pregnancy. This non-invasive detection can not only provide effective proof for the existence of male DNA in fetal DNA, but also serve as the first step to detect genetic defects related to sex chromosomes, such as mental retardation related to X chromosome.