Two day blastocysts are also called early blastocysts and are formed one to two days early in the blastocyst’s life, hence the name two day blastocysts. Blastocysts are the advanced stage of embryo formation, which normally occurs five to six days after egg retrieval. If there are more normal embryos and the quality of the embryos is good, the high quality embryos can be screened for freezing or transfer. When the embryo is formed for 1~2 days it is called early blastocyst. Culturing of blastocysts is also a screening process for embryos, which can reduce the number of embryos transferred and reduce the rate of multiple births without decreasing the rate of embryo implantation. Early blastocysts will develop into late blastocysts after 1-2 days of development, and will continue to develop for another 1-2 days before implanting into the uterine lining for further implantation. Although the success rate of blastocysts is relatively high, the in vitro culture environment is somewhat different from the natural in vivo environment, which may result in the elimination of some cleavage stage embryos that are able to implant. Transferring blastocysts allows for easier implantation, thus increasing the rate of embryo implantation and reducing the risk of multiple pregnancies. There are many advantages of embryo transfer, but the decision needs to be made based on your health and your doctor’s program.