In IVF technology, more embryos can usually be obtained in one ovulation cycle, but not all of these embryos can be utilized, and only the embryos that can be utilized are worth freezing and preserving: 1. Normal fertilized embryos: embryos formed after the combination of only one sperm and one egg, if there are multiple sperms combining with one egg at the same time and the formation of an embryo, then it belongs to the abnormally fertilized embryos, and there are chromosomal Abnormalities, can not be frozen; 2, the quality of embryos: although more embryos are obtained, the quality of each embryo is different, good or bad, the quality of embryos can be comprehensively assessed from the embryo’s developmental speed, the number of fragments and morphology of the embryo and other aspects, and only the embryos that have reached a certain level are selected for freezing, such as cleavage-stage embryos, the embryo generally develops up to the 3rd day, and it can reach 6-8 cell spheres, according to the embryo’s morphology and the number of fragments, they can also be divided into 4 grades, grade 1 and grade 2 embryos belong to the better can be frozen, while grade 3 and grade 4 embryos are of poorer quality and are generally not recommended to be preserved, the scoring of embryos at blastocyst stage is again different, mainly according to the degree of expansion of blastocysts, the number of inner cell mass and trophoblast cells, usually divided into three types: A, B and C. Blastocysts of grades A and B can be frozen, while grade C Poor blastocysts are not recommended for freezing; the speed of embryo development, for example, in blastocyst culture, good quality embryos formed within 5-7 days after egg retrieval can be frozen, while those that fail to develop into blastocysts have no value for freezing. Poor quality embryos even if fresh transfer is performed, the implantation rate and pregnancy rate are lower, after the process of freezing and thawing, the developmental ability not only can not be improved, but also will be damaged to a certain extent, and the pregnancy rate will become even lower. Therefore, selecting the embryos before freezing, saving only the valuable embryos and eliminating the poorer ones can not only improve the efficiency of frozen embryo transfer, but also alleviate the patient’s financial burden.