8-cell stage

The 8-cell stage is a period in embryonic development when the conceptus has undergone 3 cleavages from a single cell, resulting in 8 cells. In some mammals, it is at this stage of development that the individual cells begin to adhere tightly, a process called compaction. (PMID 8793055; article PDF). A single cell can be removed from a pre-compaction 8 cell embryo and used for genetic screening (PMID 15569702).