Preimplantation Genetic Diagnosis (PGD) refers to a screening technique used to diagnose genetic disorders in an embryo before its implantation. PGD is also referred to as embryo screening. This diagnosis requires an oocyte or embryo for evaluation. Hence, this screening technique is generally used in couples undergoing in Vitro Fertilization (IVF) procedure with a history of genetic disorders, hereditary disease or recurrent miscarriages. PGD can be easily conducted in IVF, as the embryo is formed outside the woman’s body in a controlled environment.
In this diagnosis, one cell is taken out from the embryo on the third day post fertilization. This cell is analyzed for chromosomal anomalies. This diagnosis can be useful to prevent the implantation of defective embryos. As this is an invasive procedure where the cells of an embryo are disturbed, you can come across several circumstances.
PGD is possible only when the oocyte is retrieved and fertilization is done under laboratory conditions. Hence, couples who want to do this PGD testing must be prepared to take the IVF treatment, which brings in hormone injections, super ovulation and other IVF-related procedures.
Though abnormality of chromosomes is analyzed in this method, entire screening for all genetic conditions is impossible; hence, it does not guarantee the absence of genetic disorders in the children born after this test. (Usually a maximum of nine chromosomes can be examined through this PGD procedure, which explains that remaining 14 pairs go untested.) Thus, an abnormal chromosome can escape this test leading to the implantation of a defective embryo. Biopsy of the embryo to retrieve one cell from it may damage the embryo, resulting in the formation of genetic disorders in the embryo.
The reason for recurrent miscarriages can be determined and traced to genetic problems. You may have to face a grim situation where you encounter the realization that completing entire gestation period is not possible because of your genetic makeup. In such circumstances, you have to decide about the disposal of those embryos.
PGD can be used to find the gender of the embryo, and hence, it raises an ethical issue of custom gender selection for achieving family balance. The cost of this diagnosis is very high, and hence it creates a wide gap between the affordable prenatal diagnosis and non-affordable Preimplantation Genetic Diagnosis for most of the couples. Another problem is that this does not get covered under any insurance policy, as PGD is still considered to be an experimental approach.
Results from the PGD may not be accurate due to mosaicism of the cells in the selected embryo. Inaccurate laboratory techniques of screening can give you a false report that lets you to either implant an abnormal embryo or to reject a healthy embryo.
Word of Caution
Due to the risks and complications of this diagnosis, it is better to choose Preimplantation Genetic Diagnosis only for unavoidable situations. For instance, couples with an established history of hereditary diseases, genetic disorders or recurrent miscarriages can prevent the implantation of abnormal embryos by means of PGD so that there is an increase in the chances of a successful pregnancy.