Cleavage Embryo

Definition - What does Cleavage Embryo mean?

A cleavage embryo refers to an embryo at the stage of its development in which it is undergoing a series of cell divisions, or cleavages. This stage begins about 24 hours after the egg is fertilized and lasts until the morula is formed around 4 days after fertilization. During in vitro fertilization (IVF), cleavage stage embryos are examined on the third day after fertilization and graded on their quality. The embryos with the best grades will be more likely to result in a successful pregnancy.

FertilitySmarts explains Cleavage Embryo

About 24 hours after an egg has been fertilized, its first division (cleavage) occurs. The result of this division is a 2-cell organism. These cells further divide, or cleave, to progress through 4-cell, 8-cell, and 16-cell stages. Each of the cells in these stages is known as a blastomere and will later go on to form a blastocyst.

Although the cells within the embryo are increasing, the embryo itself remains about the same size throughout this process. As the cells are dividing, small portions of the cell may break off and form a bleb. This is called fragmentation and can impact the quality of the embryo.

Cleavage embryos are graded during based on the number of cells they contain and their appearance under a microscope. On day 3 after fertilization, a good quality embryo usually contains 6-10 cells at this stage and contains little to no fragmentation. Embryos with the best grades will be used for transfer in hopes that they will produce a successful pregnancy.

An embryo can be transferred at the cleavage stage in what is known as a Day 3 transfer. Alternatively, the embryo will continue to grow in the lab setting until 5 days after fertilization. This allows it to develop into a blastocyst before being transferred. Health care providers have differing opinions on which type of transfer is more likely to produce a successful pregnancy.

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