It is not necessary to raise embryos to blastocyst stage for IVF, but it is determined by the specific situation of embryos. The purpose of raising blastocyst is to improve the transfer success rate, if the quality of embryos is not very good, it is better not to raise blastocyst for direct transfer. If the embryo quality is good, it is better to raise the embryo to blastocyst. Raising the embryo to 5-6 days cells increase the number of cells of the embryo through multiple divisions to increase the structural complexity and the embryo is more stable, which can increase the embryo transfer rate more, if the embryo is directly transferred without raising the blastocyst, the number of embryo cells is less and the transfer success rate is about 40%. There is also some risk in raising embryos to the blastocyst stage. Embryos have strict requirements for breeding conditions, including environment, temperature and sterility, and embryos of poor quality will not raise blastocysts.