Preimplantation genetic diagnosis, or third-generation IVF technology, includes preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS), which refers to the technology of genetic testing of embryos for the purpose of improving the success rate of IVF and producing healthy offspring, and shifting IVF technology from simply solving fertility problems to promoting eugenics. Indications The indications for PGD are single gene disorders and inherited chromosomal abnormalities. In cases where there is a clear single gene disease or hereditary chromosomal abnormality in the parental generation, the embryos obtained are genetically diagnosed to avoid the transfer of embryos with genetic abnormalities, thus blocking the genetic disease. Indications for PGS are advanced age, recurrent failure of implantation, recurrent miscarriage, and severe male infertility. PGS can be chosen to improve embryo fertility and pregnancy rate when no clear genetic disorder is found in the parental generation but there are cases of advanced age, recurrent failure of implantation, recurrent miscarriage or severe male infertility. Testing methods Early PGD/PGS was performed by taking 1-2 cells from the cleavage bulb on day 3 of in vitro fertilization for genetic analysis. Nowadays, 3-10 cells from the outer trophectoderm or polar bodies are taken from the blastocyst on day 5 or 6 for genetic testing, from which genetically normal embryos are selected for transfer to obtain a healthy next generation. Limitations Although the idea of preimplantation genetic diagnosis is promising, it is still limited by several factors in its application. 1. Safety: Biopsy may bring embryo damage, decreased implantation potential, epigenetic changes and possible long-term effects in adulthood still need more studies to demonstrate, and the idea of using embryo culture fluid for PGD/PGS proposed by some people may be a developmental direction. 2. Number of embryos, blastocyst raising and whole embryo freezing: Since the embryos have to be collected until the 5th or 6th day of development, all the tested embryos need to be blastocyst raised, and the reduction of embryo number caused by this process is inevitable, and the number of blastocysts reaches a certain amount before the test is meaningful; the time required for PGS result analysis is more than 24h, and the tested embryos need to be frozen to choose the right time for transfer. 3. Technical limitations: Some errors in the existing testing technology cannot be eliminated, and the possible existence of chimerism in embryos may cause false positives and false negatives. 4. Economic factors.