What is a Cleavage Stage Embryo?

In embryology, cleavage is the division of cells in the early development of the embryo, following fertilization. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same size as the original zygote.

IVF-created embryos generally are transferred into the uterus at either the cleavage stage or blastocyst stage. Usually, embryos contain of 4 cells on day 2 and 8 cells on day 3.