There are four blastocyst grades, grade A and B are good quality blastocysts, grade C are ready for transfer and grade D embryos need to be eliminated. In IVF, a high quality egg and sperm are selected to be combined in vitro and the blastocyst will be raised and observed for 3-7 days. If the embryos are full by the third day of development, the right time for intrauterine transfer can be chosen. If no quality blastocyst appears by the third day of embryo development, observation can be continued. By the seventh day, a full gestational sac can also be transferred. Depending on the size of the blastocyst cavity and whether it hatches or not, there are six stages of development, and when all the blastocysts hatch out of the blastocyst cavity, it proves to be the best quality embryo development. The earlier and fuller the embryo is developed, the better the grade of the embryo is and the higher the chance of transfer to the uterine cavity for growth and development, which can increase the success rate of IVF.