Embryo grade is a classification that measures the quality of the embryo and is generally categorized into four grades: A, B, C, and D. Grade A embryos are of the best quality, while grade D embryos are of the worst quality and need to be discarded. Generally, according to the growth and development of the embryo, embryos are categorized into four grades: A, B, C, and D. Grade A embryos have uniform cell division and are of good quality; grade B embryos have more uniform cell division; grade C embryos have more uneven cell division; and grade D embryos have uneven cell division. Usually, grade A, B and C embryos can be transferred normally, but grade D embryos are of poor quality and need to be discarded. After selecting good quality embryos for transfer, the embryos have a higher rate of implantation. The embryo can only develop into a normal fetus after it has been deposited in the uterine cavity. Therefore, choosing high quality embryos can improve the success rate of IVF.