Preimplantation Genetic Diagnosis: PGD

Preimplantation genetic diagnosis (PGD) is a genetic procedure used prior to implantation to help identify genetic defects within an embryo created through in vitro fertilization and to prevent certain diseases or disorders from being passed on to the child. In most cases, the female, the male, or both have been genetically screened and determined to be carriers.

How is the PGD performed?

The preimplantation genetic diagnosis begins with the normal process of in vitro fertilization which includes: ovary stimulation through medication, egg retrieval, and fertilization in a laboratory. Over the next three days the embryo will divide into 8 cells. The preimplantation genetic diagnosis involves the following steps:

A single cell is removed from the embryo using small instruments referred to as pipettes.
DNA is retrieved from this cell and copied through a process known as polymerase chain reaction (PCR).
By molecular analysis, the DNA sequence code is evaluated to determine if the inheritance of the gene is present.

Once the PGD procedure has been performed and embryos free of genetic problems have been identified, implantation will be attempted through embryo transfer, intracytoplasmic sperm injection (ICSI), or zygote intrafallopian transfer (ZIFT).

Who can benefit from PGD?

Preimplantation genetic diagnosis can benefit any couple at risk for passing on a genetic disease or condition. Below is a list of individuals who might be appropriate candidates for PGD:

Women ages 35 and over
Carriers of sex-linked genetic disorders
Carriers of single gene defects
Those with chromosomal disorders
Women experiencing recurring pregnancy loss (associated with chromosomal concerns)

PGD has also been used for the purpose of gender selection. However, discarding embryos based on gender has raised ethical concerns for many people.

What does PGD look for?

Preimplantation genetic diagnosis looks for genetic and chromosomal problems that place the couple at risk for birth defects or spontaneous miscarriage. PGD identifies the presence of the following:

Recessive sex-linked disorders: such as hemophilia, fragile X syndrome, most neuromuscular dystrophies
Dominant sex-linked disorders: such as Rett syndrome, incontinentia pigmenti, pseudohypererp arathydroidism, vitamin D-resistant rickets
Single gene disorders: such as cystic fibrosis, Tay-sachs, Huntington disease, sickle cell anemia
Chromosomal rearrangements: such as translocation, inversion, deletions and Aneuploidy

What are the benefits of PGD?

The following are considered benefits or advantages for using PGD:

The procedure is performed before implantation, reducing the need for amniocentesis later in pregnancy.
The procedure is performed before implantation, allowing the couple to elect to continue with the pregnancy or not.
The procedure enables some couples to pursue biological children who might not have otherwise.
PGD may help reduce the expenses which usually accompany medical complications by avoiding certain birth defects.

What are the concerns of PGD?

The following are considered concerns or disadvantages for using PGD:

For many people, life begins at conception and the destruction of embryos is the same as destruction of an individual. The PGD procedure usually results in a small number of discarded embryos.
In some cases, a genetically defective fertilized egg will mature and not necessarily generate the disorder or disease. The disorder development probability needs to be further discussed with your healthcare provider.
Although genetically present, some resulting diseases only develop symptoms when an individual reaches their thirties or forties.