An Intro to Preimplantation Genetic Diagnosis (PGD)

PGD or preimplantation genetic diagnosis is a form of pre-pregnancy, genetic testing for detecting genetic defects in the embryo. It is usually conducted as a part of tests during artificial insemination. PGD is applicable to embryos that are developed through in vitro fertilization or IVF. This testing technique was first applied for an IVF birth in 1989.

What Advantage Does Preimplantation Genetic Diagnosis Offer?

PGD is a less invasive way to ensure that a child is born without genetic diseases. Since PGD is performed during the pre-pregnancy stage, it provides the opportunity to identify and remove the embryos that indicate the presence of genetic disorders. Thus, only the tested embryos are transferred to the uterus of the woman undergoing artificial insemination. In comparison, other forms of genetic testing prove to be more difficult. For instance, diagnostic procedures like chorionic villus sampling and amniocentesis only provide the options of either terminating the pregnancy, or continuing with it and taking upon the risk of conceiving a child with genetic abnormalities. Either of the decisions can be physically and mentally draining for the patient and her partner.

Further, PGD has wider applicability than other forms of genetic testing. It is applicable to women:

  • Who have a history of recurrent miscarriages—it is likely that preimplantation genetic diagnosis can actually decode the reason for repeated miscarriages.
  • Who are more than 35-years-olds and are seeking IVF.

Preimplantation Genetic Diagnosis is seriously advised to couples:

  • Diagnosed with chromosomal translocations—a major cause for implantation failures and recurring miscarriages apart from inducing mental/physical disorders in the child.
  • Having a family history of chromosome X-linked disorders—this chromosomal defect raises the chances of passing-on the genetic disorder to the child by nearly 25%.
  • Where either parent is a carrier of Autosomal Recessive Diseases—these diseases have a very high incidence of being inherited across multiple generations. The risk of passing-on the disease to the embryo is nearly 25%.
  • Where either parent is a carrier of Autosomal Dominant Diseases—the risk of passing on such diseases to the embryo is nearly 25%.

PGD & PGS: Avoid the Confusion

The difference between PGD and PGS (Preimplantation Genetic Screening) should be clearly understood. Preimplantation genetic screening refers to testing of embryos when there is no known fear or cause to indicate any kind of chromosomal or genetic disorder among the parents. This is also referred to as testing for Aneuploidy or testing for an abnormal number of chromosomes in the embryo (non-genetic condition). Preimplantation genetic diagnosis refers to testing when one or both the genetic parents indicate some form of personal or family history of genetic abnormalities. It should be noted that in many clinical settings, PGS may be referred to as a PGD testing.

Question of Ethics in Preimplantation Genetic Diagnosis

The critics of this testing opine that the test seeks to interfere too much with the process of fertilization. However, the counter arguments often hinge on the fact that this testing is applicable to IVF patients, which is already an unnatural form of conceiving. Thus, any additional tests being conducted to make the entire process safer shouldn’t be argued. However, despite its many advantages, PGD is often regarded as a test to produce flawless or perfect children. Some people fear that the process of elimination of embryos that forms a part of PGD testing can be manipulated by authoritative couples as a means to “select” their offspring.