Curious about Preimplantation Genetic Testing for Aneuploidy (PGT-A)? In this webinar, Dr Elena Santiago, Gynaecologist & Fertility Specialist at Vida Fertility, Spain, breaks down everything you need to know about PGT-A — from the science behind it to the potential risks and benefits.
Dr Santiago explored key considerations before deciding if PGT-A is right for you, and what you need to know before making this important decision.
Preimplantation Genetic Testing for Aneuploidy (PGT-A) has become an important tool in modern IVF, particularly for patients of advanced maternal age or those who have experienced repeated pregnancy loss or implantation failure. In this webinar, Dr Elena Santiago, Gynaecologist and Fertility Specialist at Vida Fertility, explained how PGT-A works, when it may be recommended, and what patients should realistically expect in terms of benefits and limitations.
The session focused on helping patients understand not only what PGT-A can improve, but also why it is not suitable for everyone and must always be considered on an individual basis.
Dr Santiago explained that PGT-A stands for preimplantation genetic testing for aneuploidy. It is a laboratory technique used during IVF to analyse the chromosomes of embryos before they are transferred to the uterus.
To perform PGT-A, embryos must be cultured until day five or day six of development, when they reach the blastocyst stage. At this stage, embryos are more developed and structurally differentiated. Dr Santiago described how a blastocyst contains two main components:
the inner cell mass, which will develop into the fetus
the trophoectoderm, the outer layer of cells that will form the placenta
PGT-A involves taking a small biopsy from the trophoectoderm. This biopsy does not involve cells that will form the baby itself.
The biopsy process usually starts earlier in embryo development, often around day three, when embryologists create a small opening in the zona pellucida, the embryo’s outer shell. This opening allows trophoectoderm cells to be gently aspirated at the blastocyst stage.
Once the biopsy is taken, the embryo is frozen at the clinic. The sampled cells are sent to an external genetics laboratory, where chromosome analysis is performed. Results are typically available within two to three weeks.
According to Dr Santiago, PGT-A testing can produce several different outcomes.
Some embryos are classified as euploid, meaning they have a normal number of chromosomes. These embryos are considered suitable for transfer and offer the highest chance of a healthy pregnancy.
Others are identified as aneuploid, meaning they have chromosomal abnormalities. These embryos are not recommended for transfer because they have a very low chance of resulting in a healthy pregnancy and are associated with a high risk of miscarriage.
In some cases, embryos are classified as mosaic. Mosaic embryos contain a mixture of normal and abnormal cells. Dr Santiago explained that mosaic embryos are assessed individually, depending on the type and extent of chromosomal abnormalities. Low-grade mosaic embryos may still lead to healthy pregnancies, and decisions about their transfer are made after careful discussion between the patient, the fertility specialist, and a genetic counsellor.
There are also instances where no result or an inconclusive result is obtained. This can happen when the biopsied cells do not grow adequately in the laboratory. In such cases, clinics may recommend re-biopsy, which involves thawing the embryo, taking another sample, and freezing it again. Although this involves additional manipulation, Dr Santiago noted that successful pregnancies have occurred after re-biopsy.
Dr Santiago emphasised that PGT-A is not a universal requirement for all IVF patients. Its use is typically considered in specific situations.
One of the main indications is maternal age over 38. As women age, the proportion of embryos with chromosomal abnormalities increases significantly, which reduces pregnancy rates and increases miscarriage risk.
PGT-A may also be recommended for patients who have known chromosomal abnormalities in their own karyotype, those who have experienced recurrent miscarriages, or those with repeated implantation failure after IVF.
While PGT-A does not guarantee success, it allows clinicians to identify embryos with the highest implantation potential and the best chance of resulting in a healthy, ongoing pregnancy.
Dr Santiago explained that embryo chromosomal status is strongly linked to maternal age. From around age 35, the proportion of chromosomally normal embryos steadily declines.
Egg donors, who are usually young, may have around 60% chromosomally normal embryos. In patients under 35, this figure is closer to 50%. As age increases beyond the late thirties and early forties, the percentage of euploid embryos drops sharply, making pregnancy increasingly difficult even with IVF.
Importantly, Dr Santiago noted that when a euploid embryo is available, pregnancy rates remain relatively stable across age groups. The main challenge with advancing age is producing a healthy embryo, not the embryo’s ability to implant once identified.
One of the primary benefits of PGT-A is improved implantation and ongoing pregnancy rates in patients over 35. By selecting embryos with a normal chromosomal profile, clinics can significantly increase the likelihood of success per transfer.
PGT-A also reduces miscarriage rates. Since many miscarriages are caused by chromosomal abnormalities, transferring euploid embryos lowers the risk, particularly in older patients, where miscarriage rates are naturally higher.
Another important advantage is optimising the time to pregnancy. Dr Santiago explained that without PGT-A, patients may undergo multiple embryo transfers before achieving a successful pregnancy, especially if several embryos are chromosomally abnormal. This can be emotionally exhausting, time-consuming, and financially costly. PGT-A helps prioritise embryos with the highest potential, reducing unnecessary transfers.
PGT-A also supports the widespread adoption of single embryo transfer. By transferring one tested embryo at a time, clinics can minimise the risks associated with multiple pregnancies, which are more dangerous for both the mother and babies. Dr Santiago stressed that with PGT-A, there is no clinical justification for transferring more than one euploid embryo.
Many patients worry that embryo biopsy may harm the embryo. Dr Santiago acknowledged this concern but explained that blastocysts are robust structures composed of hundreds of cells. Removing five to ten trophoectoderm cells has minimal impact when performed by experienced embryologists.
She emphasised that PGT-A is now a well-established technique, routinely performed by trained professionals, and the risk of damage is considered low. While no medical procedure is entirely risk-free, the likelihood of harm due to a biopsy is small.
Despite its benefits, PGT-A has limitations that patients need to understand.
One disadvantage is timing. Because embryos are frozen while waiting for results, the transfer is delayed to a later cycle. For international patients, this may require two trips to the clinic. However, Dr Santiago pointed out that frozen embryo transfers are now common practice and often performed in natural or modified natural cycles, which may reduce medication use and pregnancy complications.
There is also a small risk associated with embryo manipulation. Although rare, embryos may not survive thawing or repeated biopsy. Dr Santiago stressed that such outcomes are uncommon but possible.
Another limitation is accuracy. PGT-A is highly reliable, with an accuracy rate of approximately 90 to 95 percent, but it is not perfect. False positives and false negatives can occur. In some cases, embryos classified as abnormal may have developed into healthy pregnancies, while embryos classified as normal may still have undetected abnormalities.
Finally, PGT-A increases the cost of IVF treatment. However, Dr Santiago encouraged patients to consider overall costs, noting that avoiding repeated failed transfers and miscarriages may ultimately reduce both emotional and financial burden.
Dr Santiago concluded by emphasising that PGT-A can significantly reduce miscarriage rates and improve embryo selection, especially for patients of advanced maternal age or those with repeated IVF failure.
However, it is not risk-free and not universally beneficial. Its use should always be individualised, taking into account the patient’s age, reproductive history, and genetic background.
PGT-A is a powerful tool when used appropriately, but it should never be applied automatically. Careful counselling and personalised decision-making remain essential parts of fertility care.
PGT-A is not routinely recommended in egg donation treatments because egg donors in Spain must be under 35 years old. Age is therefore not the main indication in these cases. However, PGT-A may still be suggested for patients who have experienced several unsuccessful treatments or recurrent miscarriages and wish to reduce the number of embryo transfers and achieve pregnancy as quickly as possible. In these situations, PGT-A can sometimes be beneficial.
Yes, in this situation, PGT-A may be recommended. Although other factors must always be evaluated and the embryo is not the only element involved, after several failed embryo transfers, it can be helpful to use PGT-A to increase the chances of achieving pregnancy as soon as possible.
Even in egg donation or double donation treatments with young donors, chromosomal abnormalities can still occur. In cases where patients have experienced previous treatment failures and wish to achieve pregnancy as soon as possible, PGT-A may be recommended. It is also important to evaluate whether other investigations are needed, as embryo genetics is not the only factor involved.
PGT-A has an accuracy rate of approximately 90–95%, which is considered high.
PGT-A is always discussed with the patient. Although age over 38 is generally an indication, other factors must be considered. For example, if it is a first treatment cycle or if only a very small number of embryos are expected, PGT-A may not be helpful. However, if a patient has a high AMH level and a larger number of embryos is expected, PGT-A may provide additional value. The technique is explained in detail, and the final decision is made together with the patient.
Among my patients, approximately 80–90% of women over 38 undergo PGT-A, as it is usually recommended in this age group.
There is no specific number of biopsies required. Embryologists are trained progressively, first observing colleagues and then performing the technique under supervision. PGT-A biopsy is not considered technically very difficult, but supervision by senior embryologists is very important, especially during the learning phase.
PGT has been performed for many years. Earlier techniques involved biopsies at the cleavage stage (day 2 or day 3), when embryos had very few cells, which carried more risk. Today, biopsies are performed at the blastocyst stage by taking a few cells from the trophectoderm, which forms the placenta.
There may be a small risk of slightly reducing implantation potential, but there is no evidence that PGT-A causes damage to the inner cell mass or the future child. There are no known illnesses linked to the technique.
The risk is very low, around 1%. Overall, the chance of chromosomal issues after PGT-A is approximately 5–10%, and the risk of Down syndrome within that group is even lower. Standard first-trimester screening is still recommended, and further testing such as NIPT or amniocentesis may be performed if indicated.
Yes. In patients over 38 with repeated implantation failure, PGT-A can help determine whether the issue lies with the embryo or whether other factors are affecting implantation.
Yes, but the decision must be individualised. Thawing, biopsying, and refreezing embryos may slightly reduce implantation potential, but it does not increase the risk of genetic disease in the child. For patients with many previous failures or miscarriages and no other identifiable cause, PGT-A on frozen embryos may be considered.
Yes. Once PGT-A is indicated, it is recommended to test all embryos rather than transferring some without testing. Indications include advanced maternal age, recurrent miscarriages, or implantation failure, even when parental karyotypes are normal.
Usually, between 5 and 10 cells are taken from the trophectoderm.
Both methods are possible, but ICSI is preferred in most cases as it usually improves fertilisation rates. More than 90–95% of cases are performed using ICSI.
Approximately 40% of embryos from egg donation cycles may be aneuploid. This explains why pregnancy rates are not 100% and are usually around 60–65%, even with donor eggs.
Patients can ask whether the clinic routinely performs PGT-A, how experienced the embryology team is, and whether biopsies are performed in-house or by external embryologists. Using external specialists is common in smaller clinics and is not a negative factor if transparently communicated.
PGT-A is used in approximately 30–40% of IVF cycles at our clinic, amounting to roughly 300–400 cycles per year.
No. Day 5 and day 6 blastocysts have similar implantation potential. Some embryos simply develop more slowly, and waiting until day 6 does not reduce success rates.
Implantation failure occurs in approximately 30–40% of cases, depending on individual circumstances. Miscarriage rates are lower, around 10%, and are not usually due to chromosomal abnormalities.
The rate is very low, around 1%. Blastocysts are highly resilient, and survival rates after thawing are approximately 99%, regardless of whether PGT-A has been performed.
