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Genetic testing is an increasingly common part of the IVF process. By closely examining each embryo’s genes before transfer, doctors can choose the ones most likely to result in a healthy pregnancy.
While it seems straightforward, navigating this testing can be confusing, and the stakes feel high.
Let’s dive into what we know about PGT-A (pre-implantation genetic testing for aneuploidy) and who can benefit from it the most.
What is PGT-A?
PGT-A is a way to assess and pick embryos for IVF that are most likely to result in a live birth. The testing takes place after the embryos have developed and before they are transferred back into the uterus (between steps 5 and 6 below).
There are multiple ways to gather information on embryos. One of the original ways was observation of the morphology (or shape of the embryo) under the microscope. These embryo grading systems are still used today, although there is debate on how to interpret the scores.
With advancements over time, we can now assess embryos genetically as well, furthering our ability to choose the best embryo for transfer. This PGT-A testing looks at the number of chromosomes within each embryo to determine its potential for a live birth.
Each embryo should have two copies of each of the 23 chromosomes — this is called a euploid embryo. Euploid embryos are thought to have the highest potential for live birth. Embryos with an uneven number of chromosomes are called aneuploid embryos. Aneuploid embryos are historically believed to have almost zero live birth potential and most commonly result in no pregnancy or miscarriage. A few types of aneuploid embryos can result in the birth of a child with a chromosomal abnormality, such as Down syndrome and Turner syndrome.
PGT-A is performed by taking a small sample of cells from the outside of the embryo. These samples are taken on day five or six of the embryo’s development, also known as the blastocyst stage.
The results of the PGT-A testing are usually available within two weeks. This means that the embryo must be frozen after a sample is taken, and the embryo transfer must happen in a subsequent month, once the PGT-A results have come in.
What results are possible?
The PGT-A results typically categorize embryos as euploid or aneuploid and identify the gender of the embryo.
With two copies of each chromosome, euploid embryos have a total of 46 chromosomes, including two sex chromosomes (XX for female or XY for male). Aneuploid embryos have one or more chromosomes that are either missing or extra. For example, an embryo affected with Down syndrome would have 47 chromosomes because of the extra chromosome 21.
You may see specific subtypes of aneuploid embryos on your PGT-A report. A “complex aneuploid” is one where many different chromosomes are missing or extra. A “segmental aneuploid” is one where only a segment of a chromosome is missing or extra.
Embryos can also have a mosaic result, where some cells in the sample are euploid and some are aneuploid. Whether or not to transfer mosaic embryos is a complex topic that requires discussion with your doctor and a genetic counselor.
Lastly, there may be no result or “no-call,” which means the sample was processed and tested, but they cannot definitively call the embryo euploid, aneuploid, or mosaic. After discussion with your physician, these “no-call” embryos may be retested or available for transfer; conceptually, this would be the same as transferring an untested embryo.
The test is highly accurate — a recent study using the most up-to-date testing technology suggests that the error rate is 0 to 2.4%.
Are there any drawbacks?
While PGT-A is helpful in certain scenarios, there are some major considerations to keep in mind when deciding to do it in your IVF cycle.
First and foremost, there is the possibility that all embryos from a cycle are aneuploid and therefore there are no embryos available for transfer. This means that you would have to consider another egg retrieval cycle to create more embryos to test.
Second, it’s critical to know your doctor’s policies on non-euploid embryos ahead of time. Some clinics may allow transfer of no-calls, mosaics, segmental aneuploidies, or viable aneuploidies such as Down syndrome, while others may not. So if you would consider using a non-euploid embryo, you should discuss with your doctor whether PGT-A is right for you.
Finally, the timeline for using PGT-A in an IVF cycle is an important consideration. As described earlier, PGT-A requires that the embryo be frozen and then transferred in a subsequent frozen embryo transfer cycle. This means there is no possibility for a fresh transfer. This is important because the soonest you can enter a frozen embryo transfer cycle is usually a month or two after the retrieval cycle.
Beyond that, embryos do not make it to the blastocyst stage for all patients. Remember that the embryos need to be grown to the blastocyst stage, which happens on day five or six of development. For some, particularly older patients and those with egg quality issues, the embryos stop growing at an earlier stage. These patients end up with no embryos available for testing or transfer, and they may have been better served with a fresh transfer of untested embryos on day three, instead of waiting to test on day five. The theory is that while the embryo did not survive in the laboratory setting, it may have survived in the uterus and led to a live birth.
Some claim that the PGT-A process itself can harm the embryo and reduce implantation rates. However, the studies we have on implantation rate in embryos biopsied for PGT-A do not show a decreased implantation rate. There also appears to be no impact on childbirth or the future health of the child.
How much does it cost?
PGT-A requires more laboratory supplies and increased manpower. Therefore, when it’s being performed, the IVF cycle is generally more expensive. Prices and insurance coverage vary, but usually there is a lab biopsy fee, and the genetic testing lab charges a per-embryo fee.
While more research is needed, studies suggest that there is no cost benefit to PGT-A. However, doing a cost-benefit analysis of PGT-A is challenging because it’s hard to quantify the financial impact of failed implantation, miscarriage, termination, or the costs of a child affected by an aneuploidy like Down syndrome.
That said, the cost-effectiveness of PGT-A seems to increase with age. The theory here is that for older patients, there is a higher likelihood of aneuploid embryos, so identifying euploid embryos avoids the costs associated with a failed transfer.
Who benefits most from PGT-A?
The use of PGT-A during IVF cycles has dramatically increased over the past ten years — from 14% in 2004 to 44% in 2019. Despite its increase in popularity, there is still a lot of research needed to determine whether PGT-A shortens the time to pregnancy for all patients.
You cannot study this by comparing euploid and untested embryos. Most studies show that the euploid embryo has a higher pregnancy rate and lower miscarriage rate. This is because PGT-A led you not to select the aneuploid embryos.
To really answer the question of whether PGT-A shortens the time to pregnancy, you have to compare the full experience of those who did PGT-A versus those who did not. If you added on PGT-A during your IVF cycle, did you get pregnant faster? Based on what we know about the pregnancy rates and miscarriage rates for euploid embryos, it would seem that PGT-A is faster, and some studies have demonstrated this.
However, PGT-A is not the fastest route in all cases. Consider the scenario in which you have no available euploid embryos for transfer, and you would then require additional time to do another retrieval cycle. Or consider the delay because PGT-A requires a frozen embryo transfer in a subsequent month — if you are under 35, it is more likely that your embryo is euploid and you may have been pregnant faster if you did a fresh transfer.
A large randomized trial looking at patients from the start of the IVF cycle showed that there was no difference in the ongoing pregnancy rate. This study is a step forward, although there are some limitations to it. They only ended up comparing those who had two or more embryos available for testing. So it doesn’t answer whether PGT-A is a helpful add-on for those whose embryos don’t make it to the blastocyst stage.
Are there any particular groups where we see a benefit?
When we break down the studies and look at patients by age, those over 35 may have some benefit from PGT-A because of the increase in aneuploidy with age. Above 35, if we transfer an untested embryo, we are more likely to have used an aneuploid embryo and have a transfer failure or miscarriage. Studies show an improved ongoing pregnancy rate, an improved live birth rate, and an improved implantation rate for ages 35 and up. Other studies show lower miscarriage rates for ages 38 to 44 as well.
However, these results may be biased. Older patients are more likely to be excluded or withdraw from the study because they have no embryos to test, resulting in a smaller comparison group and weakening the study. While most evidence points to a benefit for those over 35, more research is needed to confirm this.
Some logistical advantages to PGT-A may make it the right choice for you. For instance, identifying aneuploid embryos allows patients to discard aneuploid embryos and therefore avoid paying storage fees for multiple excess embryos. PGT-A can also be beneficial for those planning large families who may want to undergo additional cycles based on the PGT-A outcome from the first cycle. Knowing the PGT-A status can also be helpful if you are using a surrogate, where a miscarriage due to aneuploidy could incur significant costs. Lastly, PGT-A testing encourages doctors to transfer a single euploid embryo as opposed to multiple untested embryos, thereby decreasing the rate of twins.
What about those with recurrent pregnancy loss?
If you have had a miscarriage or recurrent pregnancy losses, you have likely heard that the overwhelming majority of miscarriages are due to aneuploidy. Knowing that PGT-A identifies aneuploid embryos, it makes sense to conclude that PGT-A would help those with recurrent pregnancy loss.
A study using the national IVF registry looked at couples with recurrent pregnancy loss. For those who did PGT-A, the transfer was more likely to result in a pregnancy, but the miscarriage rate was not reduced as expected. So, it is unclear if PGT-A reduces the miscarriage rate if you have a history of prior pregnancy losses.
Closing thoughts
Based on current data, we have not established the benefit of PGT-A as a universal add-on to all IVF cycles.
There may be some people who do benefit, including those over 35, but we need more well-designed studies to determine how big the benefit is and if this benefit outweighs the risks.
As technology continues to improve and other methods of embryo selection are developed, PGT-A likely plays some role in the decision-making process. For now, it’s not a one-size-fits-all approach, and it still needs discussion between you and your doctor about the unique tradeoffs.
The bottom line
- PGT-A (pre-implantation genetic testing for aneuploidy) screens embryos for the correct number of chromosomes to select those most likely to result in a healthy live birth. However, it requires freezing embryos and delaying transfer to a future cycle.
- The testing is highly accurate and classifies embryos as euploid, aneuploid, mosaic, or no-call.
- Potential downsides include having no euploid embryos to transfer, added costs, delayed pregnancy due to frozen transfers, and possible missed opportunities if embryos fail to reach the blastocyst stage.
- Evidence suggests the greatest benefit is for patients over age 35, those using surrogates, those planning large families, or those who wish to avoid storing aneuploid embryos; benefits for recurrent pregnancy loss remain unclear.
- PGT-A is not a universal IVF add-on; its value depends on your age, fertility history, and goals and requires discussion with a doctor.
A correction was made on September 2nd, 2025: An earlier version of this article misstated the number of chromosomes a euploid embryo has. It has 23 pairs of chromosomes, not 24.
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Just to correct a glaring error in an article about aneuploidy: a euploid embryo has 23 pairs of chromosomes, not 24.
Thank you for catching this, Lauren — we’ve just edited this!
Thanks for this article! One thing that I knew going in but didn’t really factor so it surprised me was that even if the embryo is exploit, it can still result in a miscarriage due to a lot of factors (blighted ovum, uterine environment, etc). This is explained but I think the take away, at least for me was hey it’s good so we should be good. Just an important factor that it’s not a test that guarantees a pregnancy and live birth, just increases the odds.