Cleavage-stage biopsy is generally performed the morning of day three post-fertilization, when normally developing embryos reach the eight-cell stage.

Of all cleavage-stages, it is generally agreed that the optimal moment for biopsy is at the eight-cell stage.

Zygotic transcription starts at the two-, four-, or eight-cell stage.

At the eight-cell stage, the embryo goes through some changes.

FAM40A is expressed in high levels during the blastocyst, eight-cell stage, and fetal stages of development.

When the embryo reaches the eight-cell stage, a single cell is removed and tested for genetic abnormalities.

Both this stage, called the blastocyst, and the earlier eight-cell stage, occur before the embryo implants in the wall of the womb.

When the embryos reach the eight-cell stage, one cell is removed and tested genetically, a procedure called preimplantation genetic diagnosis.

The egg is formed as one cell, with two-cell, four-cell and eight-cell stages recognisable.

These two groups become specified at the eight-cell stage during compaction, but do not become determined until they reach the 64-cell stage.