What Is a PGT-A False Positive?
A PGT-A false positive occurs when preimplantation genetic testing for aneuploidy incorrectly identifies an embryo as chromosomally abnormal when that embryo is actually capable of producing a healthy pregnancy. False positives occur primarily because PGT-A analyzes only a small sample of trophectoderm cells — the cells that form the placenta — rather than the inner cell mass cells that develop into the fetus. Because these two cell populations can carry different chromosomal makeups within the same embryo, a biopsy of the placental cells alone does not always reflect the true genetic status of the entire embryo.
🔑Key Takeaways
- PGT-A tests trophectoderm cells (future placenta), not the inner cell mass (future fetus) — a fundamental and unavoidable source of false positives.
- A landmark 2025 meta-analysis found the positive predictive value for a fully aneuploid result is approximately 89%, meaning roughly 1 in 10 "aneuploid" diagnoses may be incorrect.
- Studies suggest approximately 20–25% of transferred mosaic embryos can result in chromosomally normal pregnancies, indicating that mosaic PGT-A results do not always reflect an embryo's true genetic potential.
- ASRM's 2024 Committee Opinion does not support PGT-A as a proven universal screening test for all IVF patients, and specifically flags false positives as a known concern.
- For surrogacy journeys, however, PGT-A remains strongly recommended: with typically only 3 transfer opportunities in a 12-month agreement window, using those chances on untested embryos introduces a level of risk that far outweighs the test's limitations for most intended parents.
- The smarter question for surrogacy IPs isn't "should we skip PGT-A?" — it's "if we run out of euploid embryos, is it better to do another egg retrieval than to transfer aneuploid ones?"
If you've been through IVF — or you're preparing for a surrogacy journey that involves embryo creation — you've almost certainly heard about PGT-A. Your clinic may have presented it as a straightforward way to identify the "best" embryos before transfer. And on the surface, the logic is appealing: test each embryo's chromosomes, set aside the ones that look abnormal, and transfer only the healthy ones.
But here's what many clinics don't explain clearly enough: PGT-A is a screening test, not a perfect diagnostic tool. Like all screening tests in medicine, it can produce false positives — situations where a healthy, viable embryo is incorrectly flagged as chromosomally abnormal.
This matters enormously, because in most IVF programs, embryos labeled "aneuploid" (abnormal) are not transferred. They are discarded or frozen indefinitely. In surrogacy cycles, this means fewer embryos available for transfer, potentially more egg retrieval cycles, and in some cases, transfer windows that run out before a pregnancy is achieved.
So how often does this happen? Why? And — critically — what does it mean for your surrogacy decision-making? The science is more nuanced than the marketing language around PGT-A often suggests.
What PGT-A Actually Tests
To understand false positives, you first need to understand what PGT-A is actually sampling.
When a human embryo reaches the blastocyst stage (typically day 5, 6, or 7 after fertilization), it has two distinct cell populations: the inner cell mass (ICM), which will eventually develop into the fetus itself, and the trophectoderm (TE), the outer layer of cells that will become the placenta.
PGT-A biopsies a small number of trophectoderm cells — typically 5 to 10 — and analyzes their chromosomal makeup using next-generation sequencing (NGS) or similar technology. The ICM, the part that actually becomes your baby, is never directly tested.
This distinction turns out to be the central reason false positives exist.
[Diagram 1 — Blastocyst Cross-Section & PGT-A Sampling] The diagram shows the anatomy of a blastocyst and illustrates how PGT-A biopsies only trophectoderm cells — the future placenta — never the inner cell mass that develops into the fetus.
Why Do PGT-A False Positives Happen?
There are four main biological and technical reasons that a chromosomally normal embryo can be labeled "aneuploid" by PGT-A.
1. Confined Placental Mosaicism (CPM)
This is the most fundamental cause of PGT-A false positives — a limitation baked into the test's design. During early embryo division, the trophectoderm (TE) cell lineage and the inner cell mass (ICM) cell lineage can independently acquire different chromosomal errors, meaning the two compartments carry different genetic information from the very beginning. The result: the entire TE layer is abnormal, while the entire ICM is normal. PGT-A tests the TE, returns an "abnormal" result, and that result accurately reflects the TE's chromosomal status. The problem isn't that the test made a mistake — it's that the TE simply doesn't represent the fetus.
This phenomenon, estimated to affect 30–40% of human blastocysts depending on the detection platform and threshold used, is well-recognized in prenatal medicine as confined placental mosaicism (CPM). PGT-A cannot distinguish CPM from true whole-embryo aneuploidy, because it only tests the cells that become the placenta.
2. Embryo Self-Correction
Early embryos have a documented capacity to shed abnormal cells or correct chromosomal imbalances during development. An embryo that carries some aneuploid cells at the blastocyst stage may self-correct before or shortly after implantation. In a landmark report published in the New England Journal of Medicine, Greco et al. demonstrated that the transfer of selected mosaic embryos could result in healthy live births — directly challenging the earlier assumption that all mosaic embryos should be discarded. Subsequent case series have further confirmed healthy births from embryos initially classified as aneuploid or mosaic by PGT-A.
3. Sampling Bias (in Mosaic Embryos)
A less-discussed but important limitation: a typical biopsy samples only 5 to 10 cells from a blastocyst that contains well over 100 cells in total. In embryos that are mosaic — where abnormal and normal cells coexist — which cells happen to be sampled can determine the entire result. If the biopsy needle lands in a region where abnormal cells are concentrated, the embryo will be called aneuploid, even though the majority of its cells are chromosomally normal. In this sense, the outcome can be influenced by chance as much as biology.
4. Technical Artifacts
Even in a non-mosaic embryo where all cells carry identical chromosomes, false positives can still occur — not through sampling variation, but through laboratory error. DNA amplification from a sample of just 5–10 cells is technically demanding, and signal distortions introduced during amplification can make normal chromosomes appear abnormal in sequencing reads. Lab platform choice, software algorithms, cutoff thresholds, and biopsy technique all contribute to this variability — which is why aneuploidy rates reported across different PGT-A laboratories can differ substantially. This problem is especially pronounced for segmental aneuploidy results (partial chromosomal deletions or duplications), where studies have found that up to half of such diagnoses are discordant with whole-embryo reanalysis.
[Diagram 2 — False Positive vs. True Positive in PGT-A] The diagram illustrates the two scenarios that produce an identical "aneuploid" PGT-A result: a false positive (abnormal TE, normal ICM) and a true positive (abnormal throughout). PGT-A cannot distinguish between them.
How Accurate Is PGT-A, Really?
The most comprehensive data on PGT-A accuracy comes from a 2025 systematic review and meta-analysis published in PLOS One, which pooled results from 109 studies. The picture that emerges is more nuanced than the "99% accurate" language sometimes used in PGT-A marketing.
When PGT-A labels an embryo as fully aneuploid, that result is correct roughly 89% of the time. That means approximately 1 in 10 embryos called "aneuploid" may actually be capable of producing a healthy pregnancy. It's a high accuracy rate — but not a perfect one, and the implications of that gap matter when embryos are being discarded based on the result.
The numbers become far less reassuring for mosaic results. Studies show that approximately 20–25% of transferred mosaic embryos go on to produce chromosomally normal pregnancies — suggesting that a meaningful share of mosaic diagnoses do not accurately reflect an embryo's true reproductive potential, particularly when the level of mosaicism is low. This is why ASRM and leading fertility centers now support selective transfer of low-level mosaic embryos in appropriate circumstances, rather than discarding them automatically.
Perhaps the most striking data point comes from a non-selection study cited in ASRM's 2024 Committee Opinion (Viotti et al.): when researchers retroactively applied PGT-A to embryos that had already resulted in healthy live births, 1 in 6 of those embryos — 17.1% — would have been discarded due to mosaicism or false aneuploidy. These weren't hypothetical scenarios. They were real babies.
What ASRM and ACOG Say
The American Society for Reproductive Medicine (ASRM) — the leading professional body for reproductive medicine in the United States — addressed these concerns directly in its 2024 Committee Opinion on the Use of PGT-A:
- Scientific studies have not established PGT-A as a proven universal screening test for all IVF patients, and its value in improving pregnancy rates or reducing miscarriage across all patient groups is unconfirmed.
- There is explicit concern that one may be discarding embryos that may have resulted in healthy neonates, given uncertainty about self-correction, false-positive results, and the accuracy of mosaic diagnoses.
- Two major randomized controlled trials found that conventional IVF without PGT-A produced cumulative live birth rates that were not inferior to PGT-A-guided IVF in good-prognosis patients.
- All patients should receive thorough counseling about PGT-A's limitations — including the option of not testing — before consenting to the procedure.
ACOG similarly notes that "independent of the preimplantation genetic testing modality employed, false-positive and false-negative results are possible," and that there is "insufficient evidence to recommend the routine use of preimplantation genetic testing for aneuploidy in all infertile women."
Should Surrogacy IPs Use PGT-A?
This is the question that actually matters for intended parents planning a surrogacy journey — and it requires honest reasoning, not just a recitation of scientific limitations.
The short answer: Yes. For surrogacy, PGT-A is still the right call for most intended parents.
Here's why.
The Surrogacy Context Changes the Risk Calculus
In a typical IVF cycle where a patient carries their own pregnancy, a failed transfer is costly and painful — but it can be followed by another transfer relatively quickly, and the timeline is flexible.
Surrogacy is structurally different. A standard surrogacy agreement typically provides for three embryo transfer attempts within a 12-month window. Those three attempts represent not just dollars invested in IVF, medications, monitoring, and legal fees — they represent the time and physical commitment of a surrogate mother who has opened her life to this journey.
Wasting one or two of those precious transfer cycles on an embryo with significant chromosomal abnormalities is a real cost. Failed transfers and early pregnancy losses don't just mean a negative beta-hCG. They can mean weeks of waiting through a failed luteal phase support cycle, emotional toll on the surrogate and the IP relationship, potential complications if a chromosomally abnormal pregnancy progresses before detection, and delays to the entire journey by months.
At Ivy Surrogacy, we work closely with reproductive endocrinologists and embryology laboratories to help intended parents interpret complex PGT-A results and build a realistic embryo strategy before matching with a surrogate — because the decisions made at the embryo stage have a direct impact on the surrogacy journey's timeline, cost, and emotional arc.
The Math of "1 in 10" in a Surrogacy Context
It's tempting to read the data this way: "PGT-A has a ~10% false positive rate for fully aneuploid embryos, so maybe we should transfer them and see what happens." But this reasoning inverts the risk. The ~89% positive predictive value means that when PGT-A calls an embryo aneuploid, that result is correct about 9 times out of 10. Those embryos, if transferred, result in failed implantation, biochemical pregnancies, or miscarriages at high rates.
In a surrogacy arrangement, the question is not "could this aneuploid embryo possibly succeed?" The question is: "Is this the best use of one of our three transfer opportunities?" For the vast majority of intended parents, the answer is no.
The Real Question: What to Do When Euploid Embryos Run Out
Where the PGT-A false-positive debate becomes genuinely important for surrogacy IPs is a specific scenario: you have embryos left, but they've all been labeled aneuploid or mosaic, and you're facing a choice.
Before committing a surrogacy transfer window to an embryo with a concerning PGT-A result, consider the alternative: a new egg retrieval cycle.
A new retrieval creates new embryos — embryos that may include high-quality euploid blastocysts. The investment in another retrieval (financially and medically) may be considerably less than the cumulative cost of two failed surrogacy transfers, a stalled agreement, months of delay, and the emotional weight on everyone involved. It also preserves the surrogacy relationship and the surrogate's physical and emotional wellbeing from cycles that carry low probability of success.
We recognize that hearing "consider another retrieval" after a difficult egg retrieval process, or after receiving an entirely aneuploid cohort of results, can feel devastating. That news is among the hardest things an intended parent can face in this journey, and no amount of clinical logic makes it hurt less. If you find yourself there, please know that you are not alone, and that a thoughtful conversation with your reproductive endocrinologist and our surrogacy coordinators can help you map a realistic path forward — whether that's another retrieval, egg donation, or another strategy entirely.
The Mosaic Middle Ground
One practical middle path worth knowing: ASRM and leading fertility centers now support the selective transfer of low-level mosaic embryos in appropriate circumstances. With proper counseling, informed consent, and prenatal follow-up testing (CVS or amniocentesis), low-level mosaic embryo transfer is a recognized option when no euploid embryos are available. This is meaningfully different from transferring fully aneuploid embryos, and it is worth discussing in detail with your care team.
Questions to Ask Your Clinic Before Proceeding
"What is your clinic's policy on mosaic embryos — and do you differentiate between low-level and high-level mosaicism?" Some clinics still discard all mosaic results automatically. Given the evidence, this approach is increasingly at odds with current best practice.
"Will I be counseled about PGT-A's limitations — including false positives — before I consent?" ASRM recommends this counseling explicitly. If it isn't offered, ask for it.
"If all my embryos come back aneuploid, what are our options?" The answer reveals whether your team is prepared to help you think strategically — including whether a second retrieval cycle makes sense before committing a transfer window.
"Can I speak with a genetic counselor?" A board-certified genetic counselor — not just a clinic coordinator — can help you interpret results and make decisions tailored to your specific situation.
Expert Summary
PGT-A is a powerful but imperfect screening tool in IVF. While it can significantly improve embryo selection in many cases — particularly for patients at higher risk of chromosomal abnormalities — its limitations related to mosaicism, confined placental mosaicism, sampling bias, and technical artifacts mean that some embryos labeled abnormal may still have genuine reproductive potential. The test's positive predictive value for fully aneuploid embryos is approximately 89%, and mosaic embryo results should not automatically be treated as equivalent to full aneuploidy.
For surrogacy journeys specifically, the strategic value of PGT-A often outweighs its limitations, because transfer opportunities are limited, emotionally significant, and tied to a surrogate's time and physical commitment. The goal is not to debate whether PGT-A is perfect — it is not — but to use it as one well-informed layer of a broader embryo strategy, with full awareness of what it can and cannot tell you.
If you're planning a surrogacy journey and unsure how PGT-A results should influence your embryo transfer strategy, our team at Ivy Surrogacy can help you evaluate your options alongside experienced fertility specialists.
Frequently Asked Questions
Q: What is a PGT-A false positive?
A: A false positive occurs when PGT-A labels an embryo as "aneuploid" (chromosomally abnormal) when the embryo is actually chromosomally normal and capable of developing into a healthy pregnancy. This happens primarily because PGT-A only tests trophectoderm cells — the future placenta — which may carry chromosomal changes absent from the inner cell mass cells that actually become the fetus.
Q: How common are PGT-A false positives?
A: For fully aneuploid results, a 2025 systematic review and meta-analysis found the positive predictive value is approximately 89%, meaning roughly 1 in 10 "aneuploid" diagnoses may be incorrect. For mosaic embryo results, approximately 20–25% of transferred mosaic embryos can result in chromosomally normal pregnancies — indicating that a meaningful proportion of mosaic classifications do not accurately represent the embryo's true reproductive potential.
Q: If PGT-A has false positives, should I still use it for my surrogacy cycle?
A: For most surrogacy intended parents, yes. The ~10% false positive rate for fully aneuploid embryos means PGT-A is correct about 90% of the time — and correctly identifying truly aneuploid embryos preserves your precious transfer opportunities for embryos with the highest chance of success. In surrogacy, where agreements typically allow only 3 transfers in a 12-month window, using those chances on unscreened embryos introduces risks that, for most patients, outweigh the test's limitations.
Q: What should I do if all my embryos are labeled aneuploid or mosaic?
A: This is one of the hardest situations an intended parent can face, and it's important to acknowledge the grief of that news before moving to logistics. When you're ready, the key conversation to have is with your reproductive endocrinologist: Is another egg retrieval cycle the right next step? Would low-level mosaic embryo transfer — with full genetic counseling and prenatal follow-up — be appropriate for your situation? Are donor eggs worth exploring? The right path is deeply personal, and our surrogacy team is here to help you think it through alongside your medical team.
Q: What's the difference between a "mosaic" and an "aneuploid" embryo?
A: A fully aneuploid embryo has chromosomal abnormalities throughout its cells; the probability of a successful pregnancy is very low. A mosaic embryo has a mix of normal and abnormal cells, and the clinical picture is more nuanced. ASRM differentiates between low-level mosaicism (20–50% abnormal cells, better prognosis) and high-level mosaicism (50–80% abnormal cells, more concerning). Low-level mosaic embryo transfer is a recognized option under current guidelines when no euploid embryos are available — these embryos should not automatically be discarded without discussion.
Q: What is embryo mosaicism, and why does it cause PGT-A errors?
A: Mosaicism means different cells within the same embryo carry different chromosomal makeups. Depending on the detection method and threshold used, it's estimated to affect 30–40% of human blastocysts. When PGT-A biopsies a small sample of trophectoderm cells, those cells may happen to carry chromosomal abnormalities not present throughout the embryo — particularly not in the inner cell mass cells that will become the fetus. This is compounded by sampling bias: with only 5–10 cells biopsied from an embryo of over 100 cells, the sampled fraction may not represent the whole even in the absence of true mosaicism.
Q: Does ASRM recommend PGT-A for all IVF patients?
A: No. ASRM's 2024 Committee Opinion states that PGT-A has not been established as a proven universal screening tool for all IVF patients, and that its value in improving pregnancy rates or reducing miscarriage across all groups is unconfirmed. ASRM does note potential benefits in specific populations (such as advanced maternal age or recurrent pregnancy loss) and recommends that all patients receive thorough counseling about PGT-A's limitations before consenting.
Q: Are there newer, more accurate alternatives to trophectoderm biopsy PGT-A?
A: Research into non-invasive PGT-A (niPGT-A) — which analyzes cell-free DNA shed by the embryo into its culture medium rather than directly biopsying embryo cells — is promising. Early studies suggest niPGT-A may be less prone to mosaicism-driven errors. However, niPGT-A is not yet widely available in U.S. clinical practice and requires more validation before it becomes standard of care.
References
- Bacal V, et al. "A systematic review and meta-analysis of the diagnostic accuracy after preimplantation genetic testing for aneuploidy." PLOS One. May 14, 2025.
- Practice Committees of ASRM and SART. "The use of preimplantation genetic testing for aneuploidy: a committee opinion." Fertility and Sterility. 2024;122(3):421–434.
- Practice Committee of ASRM. "Clinical management of mosaic results from preimplantation genetic testing for aneuploidy of blastocysts: a committee opinion." Fertility and Sterility. 2023;120:973–82.
- Greco E, et al. "Healthy Babies after Intrauterine Transfer of Mosaic Aneuploid Blastocysts." New England Journal of Medicine. 2015;373(21):2089–2090.
- ACOG Committee Opinion. "Preimplantation Genetic Testing." Obstetrics & Gynecology. March 2020.
