5AA blastocyst refers to a blastocyst that has developed to stage 5 and has a dominant trophectoderm and inner cell mass. 5AA blastocysts are equivalent to A-grade embryos, which are of good quality and are the first choice for transfer selection. The 5 in 5AA blastocyst represents the period of embryonic development, development to stage 5, the hatching blastocyst, with a part of it overflowing from the zona pellucida. The first A represents the inner cell mass and trophoblast cells that are more numerous and tightly packed. The second A represents the epithelial cell layer consisting of more cells and a dense structure. All 5AA blastocysts represent good embryonic development and are high quality embryos, equivalent to grade A in embryo quality grading, and have a higher transfer success rate. If embryo transfer is needed, 5AA blastocyst embryos are preferred.