16-cell stage

The 16-cell stage is an early embryonic stage reached after successive cleavage divisions produce sixteen blastomeres from a fertilized egg.

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Cleavage (embryology): A series of rapid embryonic cell divisions that partitions the fertilized egg without increasing the embryo’s overall size. Cleavage divisions produce the sixteen cells while the embryo remains enclosed by its original coverings.
Fertilization: The fusion of sperm and egg that initiates development of a new organism. It creates the zygote from which cleavage produces the 16-cell stage.
8-cell stage: An early embryonic stage containing eight blastomeres after cleavage divisions. It usually precedes the 16-cell stage by one cleavage division.
Preimplantation genetic testing: Testing embryos created through assisted reproduction for selected genetic or chromosomal conditions before transfer. Embryo biopsy and testing can occur during preimplantation development, although sampling is not defined by a 16-cell count.
Blastomere: A cell produced by cleavage of a fertilized egg. Each of the sixteen cells at this stage is a blastomere.
Embryogenesis: The process by which an embryo forms and develops from a fertilized egg. The 16-cell stage is one point in this broader developmental process.
32-cell stage: An early embryonic stage containing approximately thirty-two cells after further cleavage divisions. It is a later cell-count landmark reached after the 16-cell stage.
In vitro fertilization: A reproductive procedure in which eggs are fertilized with sperm outside the body. Embryos produced by this procedure may be cultured through cleavage stages, including sixteen cells.
Zygote: A diploid cell formed by the fusion of an egg and a sperm. The 16-cell stage develops through cleavage of this single fertilized cell.
Morula: A compact, solid mass of blastomeres formed during early embryonic development. A 16-cell embryo is commonly described as entering the morula stage, though timing varies by species.