Genetic Testing - PGT-A
When going through an IVF journey, your fertility clinic may offer or recommend genetic testing for your embryos. PGT-A stands for Preimplantation Genetic Testing for Aneuploidy. It is a technique used to screen embryos for numerical chromosomal abnormalities, specifically aneuploidy before they are transferred to the uterus during in vitro fertilization (IVF) procedures.
A euploid embryo is an embryo that has the correct number of chromosomes and is considered a normal embryo. Aneuploidy refers to an abnormal number of chromosomes in a cell, which can lead to genetic disorders and is a significant cause of implantation failure and miscarriages in IVF. Mosaic means there is a mixture of euploid and aneuploid cells.
Some fertility practitioners are moving away from the term “abnormal”. Any embryo that isn’t euploid is technically “abnormal,” but sometimes that could mean the testing result was inconclusive or mosaic.
What is the PGT-A process?
During PGT-A testing, a few cells are extracted from the embryo, typically on day 5 or 6 of development, and are analyzed to determine if the embryo has the correct number of chromosomes. The biopsy sample will be sent to a testing lab, while your embryos remain at your fertility clinic.
Most testing is done at the blastocyst stage because the cells start to differentiate between the outer layer which become the placenta, and the inner cells which become the baby. Typically if an embryo takes longer to reach the blastocyst stage then it has a higher chance of being chromosomally abnormal. So there are debates on whether or not it is worthwhile to test an embryo that does not mature until day 7.
Why do people get PGT-A testing done?
The main purpose of PGT-A is to identify and select embryos that are euploid. By selecting chromosomally normal embryos for transfer, the chances of achieving a successful pregnancy and a healthy baby can be significantly improved.
Euploid embryos are more likely to implant successfully and result in a healthy pregnancy, reducing the risk of miscarriage and certain genetic disorders.
If your embryos are tested and determined to be aneuploidy, then it might make sense to quickly proceed with another retrieval procedure.
If you implanted a euploid embryo and did not have a successful pregnancy, this can be helpful additional information for your doctor. Your doctor will be able to focus on other fertility issues like your uterine lining, IVF protocol, etc.
However, it's important to note that PGT-A is an optional procedure and not all couples undergoing IVF will require or benefit from this testing. PGT-A is only useful if you have multiple embryos and intend to use the results. If you only have one embryo that you intend to proceed with a transfer regardless of the test result, then it might not be worth the extra investment and intervention required in the testing process.
How accurate is PGT-A testing?
It is important to note that there can be false positives or negatives. They are making assumptions about the whole embryo just by testing one little piece. The biopsy cells may be aneuploid even if there are other euploid cells in the embryo (a mosaic). In general, the accuracy of PGT-A is relatively high, with reported rates of accuracy typically exceeding 97% in detecting chromosomal abnormalities in embryos.
A genetic counsellor can help
Fertility healthcare can lead to substantial decision fatigue! There is a lot of imperfect information where you have to make judgment calls. If you proceed with PGT-A, many clinics have genetic counsellors to help you interpret the results. Here are some questions to ask your genetic counsellor:
Does it make sense for you to do PGT-A testing?
Does this clinic report mosaic results or classify them as aneuploid?
What are the follow-up options to ask after taking time to process the results?
What is the difference between PGT-A and PGT-M?
Preimplantation Genetic Testing for Aneuploidy (PGT-A) primarily screens for numerical chromosomal abnormalities, specifically aneuploidy, which is a common cause of implantation failure, miscarriages, and certain genetic disorders.
Preimplantation Genetic Testing for Monogenic/Single-Gene Defects (PGT-M) or Preimplantation Genetic Testing for Single-Gene Disorders (PGT-S) are used to comprehensively evaluate genetic issues. This type of testing is recommended for couples who are carriers of known genetic mutations that can lead to serious inherited diseases.
