Preimplantation Genetic Diagnosis:
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
1. A single cell is removed from the embryo using small instruments referred to as pipettes.
2. DNA is retrieved from this cell and copied through a process known as polymerase chain reaction
3. By molecular analysis, the DNA sequence code is evaluated to determine if the inheritance of the gene is
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
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
- 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
- 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.