PGD testing includes preimplantation genetic diagnosis (PGD) as well as preimplantation genetic screening (PGS). The theory behind PGD testing is that embryos created by IVF can be tested for genetic abnormalities or chromosome abnormalities so that only those IVF embryos without defects are placed into the uterus.
PGD testing was first used in the early 1990s for selecting female embryos in patients at risk for X-linked diseases. This type of PGD testing is known as gender selection.
PGD testing involves the analysis of either polar bodies, which are produced from eggs during the process of meiosis, or single cells (blastomeres) biopsied from embryos after fertilization.
Disorders that are caused by a mutation or abnormality in a single gene use the technique known as polymerase chain reaction (PCR), in which a small amount of DNA is amplified for analysis. This was the first technique used in PGD testing for analysis and is still used today. Diseases such as cystic fibrosis or Huntington’s disease can be diagnosed in embryos.
More commonly, IVF embryos are tested to determine the number of chromosomes present. This is called preimplantation genetic screening or aneuploidy screening since aneuploidy is the term used to decribe embryos with too many or too few chromosomes. PGD testing for aneuploidy is performed using fluorescence in situ hybridization (FISH), in which DNA probes labeled with glowing molecules called fluorochromes are able to attach to specific chromosomes. PGD technicians are then able to count how many copies of each chromosome are present. One limitation of PGD testing with FISH is that only 7–10 chromosomes can be analyzed at once, leaving many potentially abnormal chromosomes undetected before replacement into the uterus. Twenty percent of the IVF cycles in which PGD testing was used in 2001 listed aneuploidy screening as an indication for the technology.
PGD Testing programs
PGD testing adds a great deal of complexity to an IVF treatment. As such, it should only be attempted by centers that have designated a significant amount of resources to their PGD testing program. This includes reproductive endocrinologist familiar with the appropriate stimulation protocols for performing IVF with PGD testing, laboratory embryologist who have significant experience in performing polar body biopsies, blastomere biopsies and the technologies of FISH and PCR and laboratory PhDs who are skilled in the interpretation of the results.
We have reviewed PGD testing programs and can recommend the following programs as PGD Centers of Excellence
IVF1 Centrally located in Chicago, Illinois, The personnel at the IVF1 PGD laboratory in Chicago were responsible for the first PGD babies in the world and lead the world in PGD births.
The Bridge Clinic The Bridge Clinic is a private outpatient medical facility serving the needs of patients in the Thames Valley area
SISMER SISMER is a private institute which has operated in the filed of reproductive physiology and pathology since 1994.
Monash IVF Monash IVF has established clinics in key metropolitan and regional areas throughout Victoria, Queensland and New South Wales.