PRE-IMPLANTATION GENETIC DIAGNOSIS (PGD)
Pre-implantation Genetic Diagnosis (PGD) or Pre-implantation Genetic Screening (PGS) are therapies used to assist patients with known genetic issues or otherwise unexplained recurrent pregnancy loss. Known genetic problems can include gross chromosomal abnormalities that would place the couple at risk of pregnancy loss, or having a child with multiple medical conditions.. If both members of a couple are carriers of these mutations and wish to reduce the chance of an affected child, then PGD would be an option. Finally, if a couple is suffering from recurrent pregnancy loss presumed to be due to genetically abnormal conceptions, PGS might be of benefit. PGD/PGS both involve In Vitro Fertilization. On the third or fifth day of embryo development, the embryo is biopsied and assessed for the genetic
Embryo biopsy is the technique applied by the embryologist within an IVF treatment in order to remove one or more cells from the preimplantation embryos. These cells will be then further examined by a genetic/molecular laboratory in order to receive information on the genetic status of the embryos. Briefly, this technique is utilised in order to select the healthy embryos prior to their transfer in to the uterus. Embryos that are carrying genetic disorders or chromosomal aberrations will be excluded from the final selection.
The technique can be applied in different developmental stages of the preimplantation embryos. Until recently, most IVF laboratories performed embryo biopsies on Day 3 of development (6-8 cell stage). Day five biopsy is a newer approach that is gaining a lot of popularity among embryologists since it has a few advantages over the cleavage stage embryo biopsy, such as more cells to work with (more DNA), less mosaicism, no impact on embryo development, and fewer embryos to biopsy per IVF treatment. In most cases a fresh embryo transfer is not possible though. Embryos are vitrified and are transferred to a future frozen embryo transfer. In comparison, cleavage stage biopsy carries but there is an increased risk of mosaicim and possible compromise of the implantation potential of the biopsied embryos.
Embryos that are though to be free of the genetic condition are transferred back to the mother’s uterus.