Blastocyst

The stage of embryo development that is reached about 5 days after fertilization. This is the time that the embryo usually reaches the uterus, and embeds itself into the endometrium of the uterine wall.

The transfer of embryos at blastocyst stage during in-vitro fertilization (IVF), has been a more recent evolution of fertility treatment, and in many cases is considered superior to the traditional embryo transfer practised the second or third day of embryo development.