Carolina started her presentation by explaining that her IVF lab team at Clinica Tambre is divided into two parts, the andrology laboratory where all the procedures related to the semen analysis are carried out including Spermiograms, Comet fertility, Chromosperm, Sperm freezing, etc., and the IVF laboratory where the oocytes are picked up, fertilized, and embryos are taken care of including genetic testing and vitrification.
Preimplantation Genetic Testing (PGT)
Thanks to PGT testing, it’s possible to detect if the embryo has a correct genetic context or if it has any genetic alterations in the structure of chromosomes. In some cases, it’s possible to detect if it’s a carrier of a certain disease that can be transmitted from the parents. How does it work?
On day 5 of embryo culture and the following days, instead of transferring an embryo, an embryo biopsy is carried out and embryos are frozen until the PGT result arrives. How do the embryos get to day 5 of development? After the egg collection, oocytes are inseminated by conventional IVF or ICSI (Intracytoplasmic Sperm Injection) where one sperm is introduced to each egg. At this point, the embryo culture will begin. Embryo division will be supervised each day until the last day of embryo culture, which will be around day 5 or day 6. It is important to note that on day 3 of the culture, an embryologist will perform a hole in the outer layer of the embryo, which is called the zona pellucida. This allows better access to the cells that will be biopsied, this method is called Assisted Hatching. The Gardner grading system is then used, which allows for evaluating day 5 blastocysts quality. Embryos with very good quality, so letters A and B will be considered for biopsy, the aim is to obtain 3 to 5 cells from the trophectoderm, which is the outer layer of cells present in the embryo. Those cells will be sent for genetic analysis. The cells are taken with a biopsy pipette, these cells will be separated from the embryo itself using a laser, which does not harm the embryo. Once these cells are separated they are going to be introduced into a tube, the embryo is frozen, and it will remain frozen until it can be transferred, and the result is revealed.
After the biopsy is performed and the embryo is frozen, the cells will remain stocked until they are sent to the genetic laboratory. This normally does not take more than 2 days. Once the cells are sent to the laboratory, it takes approximately 15 days to get the results, in the case of PGT-A, in the case of PGT-M, it can take a bit longer, and this will be individual for each case, but it can take up to a month. After the results are ready, you will have a consultation with the doctor to discuss the results and the following steps to take.
What happens in the genetic laboratory? As soon as the cells are received, the DNA is extracted, and it is sequenced by Next Generation Sequencing (NGS), which is the latest technology in genetic sequencing, The machine reads each chromosome and can detect the different abnormalities previously described. The profile that is reported by this machine is analysed by the most experienced genetic professionals who prepare the reports and send them to the clinic.
As a result, there could be 3 different scenarios, euploid embryos, which are healthy transferable embryos that are always the first ones that would be transferred, aneuploid embryos, which do not have correct genetic content and therefore must be discarded because they cannot be considerate for a transfer, and mosaic embryos, which means embryos with correct and incorrect genetic content. These embryos may be only considered for transfer if no euploid embryo is available and after genetic counselling, where all the risks of transferring these embryos are well explained.