Human embryos can have genetic abnormalities. Genetic abnormalities can be in the form of extra or missing chromosomes or parts of chromosomes, and here’s what can happen with embryos carrying Genetic Abnormalities-
- An embryo with genetic abnormalities can form a blastocyst (embryo at day 5 or 6) and be transferred to the uterus but will later miscarry.
- Sometimes, during culture of embryos after IVF, genetically abnormal embryos will not develop.
- Embryos with genetic abnormalities can survive to birth and the most common of these is Down’s syndrome (Trisomy 21).
When embryos are formed in the laboratory, some genetically abnormal embryos may reach the stage of blastocyst. Approximately 40% of human blastocysts are genetically normal, however this reduces to 25% if the woman is aged 42 at the time the eggs were collected.
How do you test for genetic abnormalities in embryos?
Analysing the genetic composition of the embryo is called as Preimplantation Genetic Testing (PGT). PGT involves taking a biopsy of an embryo, which involves removing a tiny part of the embryo which will develop into the placenta. From this sample, the genetic make-up is tested. Within PGT there are different types of genetic testing – PGT-A, PGT-M, and PGT-SR. The most common test is PGT-A, which is PGT for Aneuploidy, which specifically looks at the number of chromosomes of an embryo.
What are the benefits of PGT-A?
Though PGT-A is unable to repair embryos, it can identify embryos that are not suitable for transfer because of underlying genetic abnormalities but have developed to the blastocyst stage and appear normal. Depending on the age of the women when the eggs were collected, approximately 60-75% of human embryos which have developed to the blastocyst stage and appear normal are genetically abnormal. Transferring an embryo after a PGT-A test, therefore, reduces miscarriage and improves pregnancy rates per embryo transferred.
If I have a PGT-A test will it increase my chances of having a baby?
This is a controversial question. It is argued that having a biopsy of embryos is traumatic and can harm a normal embryo. It is safer to have each of the embryos transferred one by one (and avoid the risk of biopsy) and let the aneuploid embryos miscarry. For some couples with many embryos, this may take a lot of time and will incur increased out of pocket costs.
Up until 2019, there had been three randomised, controlled trials had been performed internationally and all three showed increased pregnancy rate and reduced miscarriage in women over 38 years of age (as the age of the woman increases so does the risk of having an embryo with genetic abnormalities).
Couples predisposed to genetic abnormality because of their genetic makeup (called translocation) have a definite benefit from PGT-A. Approximately 1% of the population will have a normal number of chromosomes but have a rearrangement of their chromosomes (meaning one is stuck to another) and this increases the risk of having aneuploidy in their embryos to a high extent. People with rearrangements (called balanced translocations) often have a history of repeated miscarriages and benefit from PGT-A in a very significant positive way.
If you are thinking of getting the PGT-A test, be sure to ask when during the embryo development the test will be performed.
It is advisable to plan the biopsy on day 5/day 6 of an embryo (at blastocyst stage) If you’re thinking of having your embryos tested for genetic abnormalities, please speak to staff at CIFAR who will be happy to assist you with your queries.
