All embryos communicate with the parent uterus using various hormones called cytokines.

• Cytokines help the uterus to prepare for implantation.
• Embryos chemically tell the uterus what it needs for development and implantation.
• Embryo transfer on Day 3 aids the implantation of a second sequential transfer of blastocysts on day 5. This increases the chances of possible pregnancy since the uterus was prepared by the first embryos for the second set of embryos.