In recent years, with the continuous development and improvement of assisted reproductive technology (IVF), it has helped many infertile couples to successfully conceive bringing new hope to many infertile families. As with most procedures, IVF does not have a 100% success rate, but as the technology continues to mature, the success rate is becoming more and more satisfactory. This has led to a lot of curiosity about all aspects of IVF. One of the most mysterious is the blastocyst technique. In IVF, the blastocyst is the final stage of embryonic in vitro culture, usually formed on the 5th-7th day after the egg is fertilized. In its natural state, the human embryo is implanted into the mother in the form of a blastocyst. Therefore, it is not difficult to understand that blastocyst transfer is performed to obtain a high rate of embryo implantation. Advantages of blastocyst culture and blastocyst transfer: 1. Stimulating the developmental potential of embryos: whether an embryo can develop to blastocyst is related to its own genes. When an embryo has no developmental potential or carries abnormal chromosomes and genes, it can be eliminated naturally due to its own developmental abnormalities during extended culture, and only the best quality embryos can develop into blastocysts. 2. More synchronization between embryo development and endometrium: Blastocyst stage transfer can provide a natural environment closer to reproductive physiology and has a higher implantation capacity. 3.Reducing the risk of multiple pregnancies: Because of the high implantation rate of blastocyst transfer, the number of transferred embryos can be reduced. In case of high quality blastocysts, single blastocyst transfer is advocated, which can reduce the rate of multiple pregnancies. 4. Embryo culture provides sufficient time for split stage embryo biopsy for preimplantation genetic diagnosis (PGD). Disadvantages of blastocyst culture: 1. Embryo culture failure: Blastocyst culture requires high conditions, and due to laboratory culture conditions or embryos themselves, embryos may stop developing or degenerate, resulting in no embryos available for transfer. 2. More oogenic embryos may be wasted: Since the in vitro culture environment is not the natural in vivo environment after all, prolonging the culture time may degrade some of the oogenic embryos that can be implanted. Suitable population for blastocyst culture: 1. Patients with multiple failed IVF; 2. Patients with more embryos: because of high implantation rate of blastocyst transfer, it can enable patients to get pregnant as early as possible and save time and energy; 3. When the endometrium and embryo development are not synchronized: in fresh embryo transfer cycle, when progesterone is significantly elevated before egg retrieval, the endometrium development is not synchronized with embryo, and blastocyst transfer can correct this asynchrony and improve pregnancy outcome; 4. Patients undergoing pre-implantation genetic diagnosis.