Embryo at blastocyst stage.
This is how an embryo looks like five days after egg fertilisation by sperm.
The inner cell mass (ICM) can be seen clearly. On later days, it will break down the membrane protecting it and become attached to the endometrium in the woman's uterine cavity. This is known as "hatching".
This embryo is a good candidate to be transferred to the maternal uterus by means of embryo transfer.