Know More about Embryo Biopsy, PGS & PGD
What is Embryo Biopsy?one or two cells from the preimplantation embryo for the purpose of the genetic analysis is called an embryo biopsy. The procedure is similar to chorionic villus sampling or amniocentesis, as these also aim at genetic testing by means of removal of an adequate number of embryonic cells. Couples, who undergo an IVF procedure in order to get pregnant, may opt for an embryo biopsy, to allow genetic screening of their embryos for chromosomal errors, before the embryos are transferred back into the patient.
In vitro fertilization involves fertilizing the female egg with sperm in a petri dish. Multiple embryos may be formed in this process. A biopsy can be performed at any one of the following 3 developmental stages of an embryo: polar body, day 3 or day 5. Even though, traditionally, embryo biopsy used to be predominantly performed in an 8-cell embryo on day 3, now, clinical evidence is mounting in favour of performing biopsy at the blastocyst stage on day 5.
Process of a Blastocyst stage Embryo Biopsy: er is used to create a small opening in the covering layer, also known as zona pellucida, of a blastocyst stage embryo on day 5.
As the blastocyst begins to expand in order to hatch out of the zona, the trophectoderm slowly begins to herniate out of the zona pellucida through the opening created. With the help of advanced micro tools and laser, the embryo is held in place and 4 – 5 herniating cells are detached from the embryo. During the biopsy procedure, special care is taken to safeguard the embryo. Embryo biopsy is performed on all the embryos generated during IVF. After biopsy, the embryos are immediately frozen for subsequent use.
33rd day vs 5th day biopsyso be performed on the 3rd day of embryonic development when the embryo is at the 8-cell stage. In this case, 1 to 2 cells can be removed from an 8-cell embryo. This procedure requires the introduction of an opening in the zona pellucida through which a single cell can be gently aspirated for genetic analysis. However, since removal of a single cell from an 8-cell embryo may lead to a higher loss in total embryonic mass as compared to that for a blastocyst stage embryo (where 4-5 cells are removed from an embryo with ~ 150 cells), this approach may lead to a reduction in the implantation potential of the embryo.
In addition, a biopsy from a blastocyst on day 5 involves removal of trophectodermal cells (that later develop into the placenta) but not cells that form the inner cell mass, a portion of the embryo that eventually develops into the foetus. The implantation rate is higher with this approach. Trophectoderm biopsy also results in a more accurate analysis, as there is more genetic material (from 4-5 cells) available for genetic testing.