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What Is PGT-A? Genetic Testing of Embryos Before IVF Transfer

PGT-A screens IVF embryos for chromosomal number abnormalities before transfer. It identifies euploid embryos (normal chromosomes) and filters out aneuploid ones. Transferring euploid embryos can improve outcomes per transfer, particularly in older patients — but the 2024 ASRM committee opinion concluded that routine use in all IVF patients is not supported by current evidence.

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What exactly does PGT-A test?

During IVF, embryos are cultured to the blastocyst stage (typically day 5 or 6). When PGT-A is added, a small number of cells are biopsied from the outer cell layer (the trophectoderm, which develops into the placenta) and sent to a genetics laboratory. The embryo is frozen while results are awaited.

The lab analyzes the biopsy for aneuploidy — abnormal chromosome number. A euploid embryo has the correct 46 chromosomes. An aneuploid embryo has extra or missing chromosomes (such as trisomy 21, which causes Down syndrome, or monosomy X). The test screens all 24 chromosome types 1.

PGT-A does not detect: - Single-gene disorders such as cystic fibrosis or BRCA mutations (that is PGT-M, for monogenic conditions) - Chromosomal structural rearrangements such as translocations (that is PGT-SR) - All potential causes of implantation failure or pregnancy loss

It specifically identifies chromosome number abnormalities and is sometimes called comprehensive chromosome screening (CCS).

Why do chromosomal abnormalities in embryos matter?

Aneuploidy is the most common cause of IVF implantation failure and early pregnancy loss. Most aneuploid embryos either fail to implant or miscarry in the first trimester. The rate of aneuploidy in embryos increases substantially with the age of the person who produced the eggs 1.

Chromosomal abnormalities account for approximately 50–60 percent of first-trimester miscarriages, and the proportion rises to roughly 75 percent in women over 40 2. This age-related pattern explains why IVF success rates decline with age and why identifying euploid embryos for transfer is more valuable as the proportion of aneuploid embryos rises.

By screening embryos before transfer, PGT-A aims to increase the probability that each transfer involves a chromosomally normal embryo, reducing the likelihood of a failed cycle or a miscarriage before a successful pregnancy is achieved.

Who is most likely to benefit from PGT-A?

The 2024 ASRM committee opinion on PGT-A concluded that its routine use in all IVF patients cannot be recommended based on current evidence, including randomized controlled trials showing similar overall pregnancy outcomes between PGT-A and conventional IVF 1. However, the opinion identified specific patient groups where benefit is more plausible:

Older patients (particularly 38 and above). The higher background aneuploidy rate means PGT-A provides more meaningful selection benefit. Post-hoc analyses of RCTs have shown increased ongoing pregnancy rates per transfer in older patients, even when cumulative live birth rates are similar.

Recurrent pregnancy loss. Since chromosomal abnormality is the most common cause of early miscarriage, selecting euploid embryos can reduce loss rates in people with a history of multiple losses. The updated 2026 ASRM committee opinion on recurrent pregnancy loss recommends offering genetic evaluation of miscarriage tissue to all patients 2.

Recurrent implantation failure. If two or more embryo transfers have failed, PGT-A can help determine whether the embryos themselves were chromosomally normal, and if they were, shift the investigation toward uterine or other factors.

Patients who strongly prefer single-embryo transfer. PGT-A may support the selection of a known-euploid embryo for SET, reducing multiple-pregnancy risk.

For younger patients (under 35) with good ovarian reserve and no history of recurrent loss or failed transfers, the incremental benefit of PGT-A is smaller, and the 2024 ASRM opinion explicitly notes it should not be offered routinely to this group 1.

What the current evidence shows about overall outcomes

The central question — does PGT-A improve cumulative live birth rates compared to conventional IVF? — has been addressed in several multicenter randomized controlled trials. The 2024 ASRM committee opinion reviewed this evidence and concluded that "frozen embryo transfer outcomes were similar between PGT-A and conventional IVF" in trials that included patients across age groups 1.

The explanation is that PGT-A shifts when a successful pregnancy is achieved (earlier, by avoiding aneuploid transfers) without necessarily increasing the total number of live births, because the same euploid embryo would eventually be transferred in the conventional arm. The per-transfer success rate is higher with PGT-A; the cumulative rate is more similar.

This distinction matters clinically: for a patient with many embryos and time to spare, cumulative outcomes may be the relevant metric. For a patient with limited embryos or age-related urgency, improving per-transfer efficiency may be the priority.

What are the limitations and things to consider?

PGT-A is a meaningful tool in selected patients, but it has real limitations:

Mosaic embryos. Some embryos are mosaic — a mix of euploid and aneuploid cells. These are challenging to classify, and the ASRM’s 2023 committee opinion on mosaic results notes that results can be reported differently across laboratories for the same biopsy 3. Most clinics recommend detailed counseling before transferring a mosaic embryo.

It does not guarantee a live birth. A euploid embryo still fails to implant in a meaningful proportion of transfers. Chromosomal normalcy is necessary but not sufficient for a successful pregnancy.

Biopsy risk. The trophectoderm biopsy carries a small risk of damaging the embryo. In experienced hands this risk is low, but it is real and should factor into the decision.

Cost. PGT-A adds significant cost to an IVF cycle — typically several thousand dollars — that is generally not covered by insurance.

False positives and false negatives. No genetic test is perfect. A small percentage of results may be inaccurate.

The decision about whether to pursue PGT-A is best made with your reproductive endocrinologist, who can frame the benefit-and-risk calculation for your specific age, diagnosis, and history 1.

Common questions

Does PGT-A improve my chances of having a baby overall, or just per transfer?

The evidence is more consistent for improving outcomes per transfer (fewer failed transfers and fewer miscarriages before achieving pregnancy) than for improving cumulative live birth rates overall — particularly in younger patients. The 2024 ASRM committee opinion found that overall pregnancy outcomes in multicenter RCTs were similar between PGT-A and conventional IVF. For older patients and those with prior failed cycles, the per-transfer benefit may be more meaningful.

What happens to embryos that test as aneuploid?

Aneuploid embryos are typically not transferred. They may be discarded, kept in storage, or in some cases donated for research. Some clinics offer options for transferring low-level mosaic embryos in specific circumstances after detailed counseling from a genetic counselor.

Is PGT-A the same as PGT-M or PGT-SR?

No. PGT-A screens for chromosome number abnormalities (aneuploidy). PGT-M screens for specific single-gene disorders such as cystic fibrosis or hereditary cancer syndromes. PGT-SR screens for chromosomal structural rearrangements such as translocations. Your RE and a genetic counselor can advise on which type is appropriate for your situation.

Do I need to see a genetic counselor before deciding on PGT-A?

A conversation with a board-certified genetic counselor specializing in PGT is particularly valuable if you have a family history of a genetic condition or chromosomal rearrangement, or if your embryos receive mosaic results. The 2023 ASRM committee opinion on mosaic results specifically recommends genetic counselor involvement for mosaic transfers. For standard PGT-A decisions, many reproductive endocrinology practices provide the necessary counseling directly.

Does PGT-A reduce the risk of miscarriage?

Yes, in the sense that chromosomal abnormality accounts for the majority of first-trimester miscarriages, and transferring a confirmed-euploid embryo reduces the risk of a chromosomally driven loss. However, a euploid embryo can still miscarry for other reasons, so PGT-A does not eliminate miscarriage risk entirely.

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Important considerations before pursuing PGT-A

  • —PGT-A should be discussed, not assumed — ask your RE whether it is indicated for your specific age and history
  • —Understand that a euploid result does not guarantee a successful transfer or live birth
  • —Mosaic embryo results require specialized genetic counseling before transfer decisions are made
  • —The 2024 ASRM opinion found routine PGT-A use in all IVF patients is not supported by current evidence

This article provides general information about PGT-A and does not constitute a recommendation to pursue or decline genetic testing. Treatment decisions should be made with a reproductive endocrinologist and, where appropriate, a board-certified genetic counselor.

References

  1. 1.Practice Committees of the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology (2024). The use of preimplantation genetic testing for aneuploidy: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2024.04.013 ✓2024 ASRM guidance on PGT-A: who benefits, who does not, the conclusion that routine use in all IVF patients cannot be recommended, and RCT evidence showing similar overall pregnancy outcomes with and without PGT-A
  2. 2.Practice Committee of the American Society for Reproductive Medicine (2026). Recurrent pregnancy loss: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2026.00127 ✓Chromosomal abnormalities account for approximately 50-60% of first-trimester miscarriages, rising to ~75% in women over 40; recommends genetic evaluation of miscarriage tissue for all patients with recurrent pregnancy loss
  3. 3.Practice Committee of the American Society for Reproductive Medicine (2023). Clinical management of mosaic results from preimplantation genetic testing for aneuploidy of blastocysts: a committee opinion. Fertility and Sterility. link ✓Laboratory thresholds for mosaic classification differ across labs; board-certified genetic counselor involvement recommended before transfer of mosaic embryos; mosaic embryos show reduced implantation and higher miscarriage rates vs euploid embryos

3 sources, numbered by first appearance. General health information, not medical advice — synthetic demonstration content.