Preimplantation Genetic Testing for Aneuploidy (PGT-A) or for Monogenic disorders (PGT-M) refers to a procedure where embryos obtained through an IVF cycle are evaluated for genetic disorders prior to implantation. The purpose of these tests are very different from each other. PGT-A is to identify embryos affected by chromosomal abnormalities that will affect an embryo by chance. PGT-M is to help prevent certain diseases or disorders from being passed on to the child from the parent. In most cases for PGT-M, the female, male, or both partners have been genetically screened and identified to be carriers of potential problems.
The Ottawa Fertility Centre works with a reputable genetics lab in Detroit, Michigan called Cooper Genomics . Patients of the Ottawa Fertility Centre now have access to important genetic testing prior to an embryo transfer.
What information will PGT-A provide?
- Full aneuploidies (complete extra or missing chromosome)
- Partial aneuploidies (extra or missing pieces of chromosomes)
What information will PGT-A NOT provide?
- Balanced chromosomal rearrangements, where the correct amount of genetic tissue is present
- Very small deletions or duplications of genetic material
- Intellectual disability
- Birth defects
- Single gene disorders
What are the possible results of PGT-A?
|- Euploid – No abnormalities detected|
|- Mosaic – Full or partial chromosome missing or extra in SOME cells but not all|
|- Non-mosaic deletion/duplication – Partial chromosome missing or extra in all cells|
|- Aneuploid - Full chromosome extra or missing|
|- Inconclusive/No results|
PGT-A Pros & Cons
|- Reduces miscarriages||- Chance of no normal embryos|
|- Reduces aneuploidy detection during or after pregnancy||- Test error (false negatives & positives)|
|- Less wasted time if high embryo number||- Uncertain/unclear results|
|- Risk of biopsy/freezing|
|- Does not increase overall fertility|
Who might choose to pursue PGT-A?
Reasons a couple might choose to use PGT-A can vary:
- Reduce chance of a multiple pregnancy
- Reduce time to a live birth
- Reducing risk of spontaneous abortion (miscarriage)
- Use of a gestational carrier
- Embryo banking for the future
What information will PGT-M provide?
- Presence or absence of a specific genetic difference (“mutation”) that runs in the family
What information will PGT-M NOT provide?
- Autism/Intellectual disability/Birth defects UNLESS it is caused by a specific gene being tested
- Other single gene disorders
- Chromosomal aneuploidy (but this can be added with PGT-A)
What are the possible results of PGT-M?
|- Familial genetic variant is not identified (Not affected)||- Familial genetic variant is identified (Affected)|
However, it is important to consider that the meaning of “affected” can be different. Some family members may have the same mutation but individuals may be affected differently, such as:
- Age of onset
- Effect on different sexes differently
- Be a carrier of a condition versus affected by it
PGT-M Pros & Cons
|- Identify embryos affected by a known familial genetic difference to avoid transfer of an “abnormal” embryo||- Requires customized test development for EVERY patient|
|- Often involves relatives|
|- Longer timeline (may take several months)|
|- Not always possible to identify the genetic variant|
|- Variants of unknown significance (VUS) – mutations that we don’t know what the clinical outcome may be|
Any couple at risk for passing on a genetic disease or condition could benefit from PGT-M. Possible candidates include:
- Carriers of sex-linked genetic disorders.
- Carriers of single gene defects.
- Those with chromosomal disorders.
- Women experiencing recurrent pregnancy loss associated with chromosomal concerns.
- PGT enables couples to pursue biological children who might not have been able to do so otherwise.
- Performing PGT-A or M prior to implantation can reduce the use of amniocentesis later in pregnancy.
- PGT helps reduce the chance of conceiving a child with a genetic factor. However, it cannot completely eliminate this risk. In some cases, further testing during pregnancy is recommended to ascertain if a genetic factor is still possible.
- Information and Resources
Contact your physician at the Ottawa Fertility Centre for more information and to determine whether or not PGT-A/PGT-M is an appropriate treatment option for you.