Blastomer: Definition, Uses in In Vitro Fertilization and Excision and Formation of Blastocysts

It is a cell that is created in the early stages of the division of a fertilized egg.

During in vitro fertilization (IVF) , blastomeres are used for a number of important procedures, including embryo triage and blastomere biopsy.

Blastomeres are created in the first stage of embryonic development when the fertilized egg transits from 1 cell to 2 cells, 4 cells, 8 cells and 16 cells through a process called cell division.

These divisions are called dividing divisions, and the cells created by each stage of division are called blastomeres.

Blastomere evaluation

During IVF procedures, blastomeres are evaluated through a process called embryo sorting.

The embryo classification process allows scientists and clinicians to determine how embryos are developing and which ones are best suited for transfer from the uterus.

This procedure is completed to increase the chance of a successful IVF round. Embryo triage is a standard component of an IVF procedure.

Blastomeres are also used for blastomere biopsy, also known as embryo biopsy. This procedure is performed as part of the preimplantation genetic test (PGS) on a 3-day-old embryo, which involves scientific testing during stages 4, 6, and 8 cells.

The blastomere biopsy can indicate if there are chromosomal abnormalities or genetic defects in the developing embryo.

This is a voluntary procedure that is normally only performed if the embryos are considered at risk for adverse conditions, based on the maternal age, the history of previous pregnancies, and the health conditions of the parents.

Excision and formation of blastocysts

The embryo of a cell undergoes a series of cleavage divisions, progressing through the stages of 2, 4, 8 and 16 cells. Cells in cleavage stage embryos are known as blastomeres.

Note that the blastomeres in this embryo, and the eight-cell embryo, are clearly round

At first, the cleavage splits occur quite synchronously. In other words, both blastomeres in two cells undergo mitosis and cytokinesis almost simultaneously.

For this reason, retrieved embryos are most often seen at two, four, or, and are seen here, at the eight-cell stage.

Embryos with an odd number of cells are seen less frequently, simply because these states last for a relatively short time.

Soon after the development of the 8- or 16-cell embryo (depending on the species), the blastomeres begin to form tight junctions with each other, leading to the deformation of their round shape and the formation of a mulberry-shaped mass of cells. called morula.

This change in the shape of the embryo is called compaction.

It is difficult to count the cells in a morula. The formation of binding complexes between blastomeres gives the embryo and the exterior and interior. The outer cells of the embryo also begin to express a variety of membrane transport molecules, including sodium pumps.

One result of these changes is an accumulation of fluid within the embryo, signaling the formation of the blastocyst. An early blastocyst, containing a small amount of blastocelic fluid.

As the blastocyst continues to accumulate blastocelic fluid, it expands to form an expanded blastocyst. The blastocyst stage is also a milestone in that this is the first time that two distinctive tissues are present.

A blastocyst is made up of a hollow sphere of trophoblastic cells, within which is a small group of cells called the inner cell mass.

The trophoblast continues to contribute to the fetal membrane systems, while the inner cell mass is primarily destined to develop into the embryo and fetus.

In the expanded blastocyst shown here, the inner cell mass is the dense-looking area at the bottom of the embryo.

Eventually, the stretched zona pellucida develops a crack and the blastocyst escapes through a process called hatching. This leaves an empty zona pellucida and an unzipped or streaked blastocyst found in the lumen of the uterus.

Depending on the species, the blastocyst either undergoes implantation or is rapidly lengthened to fill the uterine lumen.