Embryos implant on their sixth or seventh day of development, that is, 6-7 days after fertilization. Therefore, if the embryos are transferred on day 3, they will have to continue developing for a few more days in the uterus until they can implant.
On the other hand, if they are transferred on day 5, they will have already reached the blastocyst stage necessary for implantation to take place and will be able to begin to establish contact with the endometrium.
Read the full article on: Embryo transfer: when and how is it done? ( 79).
Degree in Biochemistry and Molecular Biology from the University of the Basque Country (UPV/EHU). Master's Degree in Human Assisted Reproduction from the Complutense University of Madrid (UCM). Certificate of University Expert in Genetic Diagnosis Techniques from the University of Valencia (UV).