The Patient's Guide to Embryology

PGT-A – Are my embryos at risk?

Embryos are surprisingly resilient but there are still some risks associated with PGT-A including damage to the embryo, misdiagnosis and long term effects to the baby.

What is PGT-A?

Preimplantation genetic testing for aneuploidy (PGT-A) is an optional add-on treatment which is becoming increasing popular in IVF. It tests whether embryos have the correct number of chromosomes which helps to identify the ones that are most likely to be successful and eliminates embryos which would never be able to make a healthy pregnancy. Chromosome abnormalities are surprisingly common and they are thought to be the biggest cause of IVF failure as well as a leading cause of miscarriage.

How is an embryo biopsy done?

To test an embryo’s DNA, cells need to be removed and sent to a specialist lab to be analysed. The best time to take a biopsy is 5-6 days after fertilization. At this point the embryo reaches the blastocyst stage and is made up of hundreds of cells, so taking a few for testing has little/no effect on the embryo’s development.

1-2 days before the biopsy, a small hole is made in the shell surrounding the embryo called the zona pellucida. This allows a group of cells to push themselves out through the gap as the embryo expands. Approximately 4-8 of these cells are removed using a tiny pipette. The cells are immediately frozen and sent to a genetics lab to be analysed and the biopsied embryo will also be frozen until the results come back. Testing the embryo’s DNA will show whether the embryo is chromosomally normal (euploid), abnormal (aneuploid) or partially abnormal (mosaic).

What are the risks of PGT-A?

There are always risks associated with genetic testing because the biopsy procedure is fairly invasive. The less an embryo is handled the better and a biopsy puts it under significantly more stress than it would experience in the body in a natural pregnancy. As well as the actual biopsy procedure, the embryo also has to be frozen while the results are processed which is additional exposure to stress. Luckily, embryos are surprisingly resilient and large studies have shown that the biopsy-freezing process doesn’t seem to have any serious detrimental effects to their potential to form a pregnancy. There are, however, still some risks associated with PGT-A:

Damage to the embryo

There are a number of different methods of removing cells from an embryo but all of them are fairly invasive. Some of the most common methods include using a laser to detach the cells or by using a combination of pulling and flicking to prize the cells away. Any form of biopsy creates stress on the embryo and has the potential to impact the quality, however, the procedure is only carried out by the most experienced embryologists and the likelihood of physical damage is relatively low.

An embryo biopsy is usually taken 5-6 days after fertilization at the blastocyst stage. It is thought that this is the safest stage because the embryo is made up of hundreds of cells so taking a few for testing shouldn’t impact its ability to keep developing. However, some embryos just aren’t able to survive the procedure. Poor quality blastocysts often have a low number of cells or the cells are showing signs of degeneration which can make a biopsy more risky and may impact its survival. You should discuss the quality of your embryos with the embryologist and decide together whether the embryos are suitable to be put through the procedure, and then have a good chance of implanting after the freezing/thawing procedure.

Long term impact

There is still a small concern that PGT-A may cause long term implications to the baby later in life. This is an area that is very difficult to research because really only time will tell. The oldest IVF baby hasn’t even reached her 50’s yet so no data exists on the long term effects of IVF, and the long term effects of PGT-A are of particular interest because removing cells from the embryo is reasonably invasive. The main concern is that biopsying an embryo has the potential to cause underlying genetic alterations which increase a person’s susceptibility to diseases in adulthood.


The technology used to analyse DNA is very advanced but there is still a small risk of misdiagnosis. Around 1% of abnormal embryos are wrongly diagnosed as normal so it is still recommended to have prenatal testing during pregnancy. There is also the risk that normal embryos will be discarded because they are wrongly diagnosed as abnormal, or because a sampling error means the removed cells were not a true reflection of the whole embryo. This is something that is improving all the time as the process and the technology keeps developing.

Cancelled cycle

The aim of PGT-A testing is to have a transfer with a normal, healthy embryo, but it can feel like an uphill battle to get there with the looming possibility of the cycle being cancelled at any point. To have the best chance of success you need to have a good number of eggs collected, good fertilization, the embryos need to reach the blastocyst stage, embryo quality needs to be suitable to survive biopsy and freezing, and there is no guarantee that the embryos being tested will be euploid (normal). Typically around 30-40% of embryos are reported as euploid but this figure decreases as female age increases. In the event that there are no blastocysts suitable to biopsy or there are no euploid embryos available, unfortunately the cycle will be cancelled and you will need to start again.

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