After the blastocyst is transferred in an IVF process, the implantation occurs when an embryo attaches the uterus wall into the endometrial lining. In the process of IVF procedure, it occurs after six to ten days after the egg retrieval process. Transferring blastocysts rather than early stage embryos takes more time to monitor the embryo's quality.
My gynecologist had mentioned that blastocyst transfer in IVF procedure plays an important role because then it guides in timely implantation of embryo in uterus. The embryo implantation is crucial for achievement of pregnancy.