Assisted Reproduction Techniques (ART) have evolved over the past decade to improve the success rates in IVF techniques. With the introduction of Preimplantation Genetic Testing (PGT), a new technique was born in laboratories – embryo biopsy.<\/p>\n\n\n\n
Embryo biopsy techniques are always improving, and have become safer and more reliable. The tools and technologies of genetic study have changed and have been replaced by more complex and accurate techniques. These changes include the way in which biopsy is performed as well as the stage of embryo development at which the biopsy is done.<\/p>\n\n\n\n
In order to perform the PGT testing we need to obtain genetic material from the embryo for analysis. A biopsy is required and this procedure consists of the removal of cells which will be discussed in this article.<\/p>\n\n\n\n
PGT and embryo biopsy techniques enable us to proceed to IVF with the confidence that we have chosen the best embryos for a successful pregnancy without genetic abnormalities and diseases.<\/p>\n\n\n\n
PGT is a genetic test performed in embryos to screen for chromosomal abnormalities or inherited diseases. Abnormal embryos are identified and the Embryologist can select genetically normal embryos for the transfer.<\/p>\n\n\n\n
Depending on the patient\u2019s medical history, the best option of PGT will be chosen for the benefit of the patient.<\/p>\n\n\n\n
Preimplantation genetic testing for aneuploidy (PGT-A): <\/strong>testing for abnormal chromosome number. This test analyses the 46 chromosomes to look for extra or missing chromosomes, such as Down syndrome (three copies of chromosome 21).<\/p>\n\n\n\n Preimplantation genetic testing for monogenic disorders (PGT-M): <\/strong>testing inheritable genetic conditions in the family to avoid passing it on to their baby, including sex-linked diseases (e.g. Cystic fibrosis or Huntington\u2019s disease). Preparation tests like bloods or saliva samples may be necessary before the PGT-M cycle.<\/p>\n\n\n\n Preimplantation genetic testing for structural chromosomal rearrangements (PGT-SR):<\/strong> genetic test performed to screen if the embryo has chromosomes arranged abnormally or are not sized correctly. This is caused by balanced translocations and inversions in the chromosomes. Chromosome rearrangements can be inherited or happen spontaneously.<\/p>\n\n\n\n Over the years, the biopsy technique has evolved. It was common to perform biopsy on day 3 of embryo development, when the embryo is in cell stage.<\/p>\n\n\n\n Several difficulties arise from performing biopsy at cell stage. If the cell lysed during the procedure, another cell will have to be removed. It is a more invasive method for day 3 embryos as there are eight cells present in the best of cases.<\/p>\n\n\n\n Not only does the technique pose challenges, but also do the results. This is because we know the chromosomal information of one cell only. The risk is lower and the results more reliable with the blastocyst stage. Embryos that have reached the blastocyst stage are currently preferred for embryo biopsy (on day 5 or 6, some laboratories even day 7, post-insemination).<\/p>\n\n\n\n The blastocyst consists of two types of cells, polarized cells become the trophectoderm, which forms the placenta, and apolar cells become the inner cell mass, which develops into the baby. The trophectoderm is the cell layer that comprises the wall of the blastocyst; the cells of the trophectoderm are the ones that we obtain from the biopsy for the genetic study.<\/p>\n\n\n\n Blastocyst biopsy has the advantage that has a larger number of trophectoderm cells. Therefore, a group of cells is studied; we obtain more information compared to the biopsy on day 3. The trophectoderm of a good quality blastocyst has many cells, between 100-300 cells. We need 5-10 cells for the genetic study. As the trophectoderm has a good number of cells; this is not harmful to the embryo.<\/p>\n\n\n\n The removal of the trophectoderm cells is possible without affecting the inner cell mass from which the future baby later develops. Obtaining around that number of cells, we will be able to obtain a result that will indicate the complete chromosomal state of the embryo. It is important that the embryo is of good quality to be able to obtain that number of cells and the embryo can continue to develop as intended. For embryo biopsy, a small incision (assisted hatching) is made in the zona pellucida that covers the embryo, on day 3 of development. This makes it easier for the blastocyst to hatch from the zona and facilitate the biopsy.<\/p>\n\n\n\n Some laboratories perform the assisted hatching on the same day as the biopsy. This depends on the routine protocol used in the laboratory, or on the embryologist, both methods are safe.<\/p>\n\n\n\n On the other hand, an exhaustive training by the Embryologist is carried out. A qualified Embryologist will perform the biopsy, and the possibility of damaging the embryo is minimal.<\/p>\n\n\n\n However, there is always some risk that damages to the embryo can occur during the procedure. This is because it is still an invasive technique, but with a good embryo quality and the right hands, the risk is minimized.<\/p>\n\n\n\nWhat happens in the lab?<\/h2>\n\n\n\n
Biopsy procedure<\/h3>\n\n\n\n