Blastomere biopsy
Blastomere biopsy (also known as embryo biopsy) is a technique that is performed by removal of one or two cells (blastomeres) from the 4 to 8 cell pre-embryo stage for the purpose of preimplantation analysis. The egg will typically be fertilized by using intracytoplasmic sperm injection or ICSI. Following fertilization, the zygote begins to divide.
On the third day following the egg retrieval, the embryo is at the blastomere stage, and a cell may be carefully removed for genetic analysis. With the embryo maintained in position by a pipette with rounded margins, an opening is performed in the embryo by using a laser device or thyroid acid: Once realized the hole, a new micropipette having a greater diameter than the first is positioned: this will consent, by means of aspiration, the removal of a cell(s) that will be then be released by applying negative pressure. At this early point of embryo development, all of the cells are equivalent and thus, removal of a cell from the embryo at this stage does not remove anything critical for normal development. The embryo compensates for the removed cell and should continue to divide following blastomere biopsy. Therefore, if the technique is carried out correctly, there are no risks for the embryo.
After removal of the cell(s) from the blastomere, the developing embryo is placed back into the culture dish and the removed cell(s) is inserted into a test tube for subsequent genetic analysis.
Polar Body Removal
As indicated above, the first polar body is produced from the division of the egg and can be removed and tested for its chromosome complement or to identify whether it contains the abnormal gene of concern.
Upon penetration of the egg by the sperm (fertilization), but prior to the joining of the sperm’s genetic material with the egg’s genetic material, the egg undergoes another cell division, producing two unequally sized cells. The larger cell will join with the sperm’s genetic material to create the pre-embryo, and the smaller cell is called the second polar body. The polar bodies have no known function except to assist in cell division. They are simply “by-products” of the egg’s division. Once implantation occurs, the polar bodies disintegrate and are not part of the developing fetus.
By testing the first and second polar bodies, the genetic make-up of the egg, and maternal genetic contribution in the resultant embryo, can be determined. Removal and genetic analysis of the polar bodies occurs on the first and second day after aspiration. In some instances, it is necessary to confirm a diagnosis made on polar body analysis by performing blastomere biopsy. It is also possible that one or more polar bodies fail to provide a conclusive result. In these situations, it may be possible to perform blastomere biopsy (embryo biopsy) for further genetic analysis.