What Is PGT-A (Preimplantation Genetic Testing for Aneuploidy)?
PGT-A, or Preimplantation Genetic Testing for Aneuploidy, is a laboratory technique used during in vitro fertilization (IVF) cycles to screen embryos for the correct number of chromosomes before they are transferred to the uterus. Sometimes also referred to as PGS (Preimplantation Genetic Screening), PGT-A helps identify embryos that are either euploid (with the normal number of chromosomes) or aneuploid (with extra or missing chromosomes). By selecting euploid embryos, the goal is to increase the chance of a healthy pregnancy and reduce the likelihood of miscarriage or chromosomal disorders such as Down syndrome.
PGT-A is performed on embryos typically at the blastocyst stage (day 5 or 6 after fertilization) via a biopsy of several cells from the embryo’s outer layer (trophectoderm). These cells are genetically analyzed for chromosomal abnormalities, guiding clinicians and intended parents in choosing which embryos to transfer.
Key Takeaways
- PGT-A stands for Preimplantation Genetic Testing for Aneuploidy and is performed on embryos during IVF.
- The test screens embryos for chromosomal abnormalities, identifying euploid (normal chromosome number) and aneuploid (abnormal chromosome number) embryos.
- Selecting euploid embryos may increase IVF success rates and lower the risk of miscarriage or genetic disorders.
- PGT-A is performed via an embryo biopsy on day 5 or 6, followed by advanced genetic analysis.
- PGT-A is often recommended for people with advanced maternal age, recurrent pregnancy loss, or previous IVF failures.
- Mosaic embryos—those with a mix of normal and abnormal cells—are a special consideration in PGT-A decision-making.
- PGT-A does not test for single gene disorders; for that, a different test (PGT-M) is used.
- PGT-A involves additional costs and may not be necessary or beneficial for every patient.
- Success rates, accuracy, and insurance coverage for PGT-A vary by clinic, patient characteristics, and laboratory protocols.
- Results of PGT-A should always be discussed with a fertility specialist and a genetic counselor.
Table of Contents
- What Is PGT-A (Preimplantation Genetic Testing for Aneuploidy)?
- Why Is PGT-A Used in Fertility and IVF?
- How Does PGT-A Work? The Testing Process Explained
- What Are Euploid and Aneuploid Embryos?
- PGT-A vs. PGT-M: Key Differences
- Indications: Who Might Benefit from PGT-A?
- What Does PGT-A Cost, and Is It Covered by Insurance?
- Success Rates and Clinical Outcomes with PGT-A
- PGT-A Accuracy, Limitations, and Mosaicism
- Risks, Benefits, and Controversies of PGT-A
- Risks vs. Ways to Reduce Risk: Summary Table
- Process and Timeline: What to Expect with PGT-A
- When to Talk to a Specialist or Genetic Counselor
- Frequently Asked Questions About PGT-A
- References and Further Reading
- Disclaimer
Why Is PGT-A Used in Fertility and IVF?
PGT-A is most commonly used in the context of IVF to help identify embryos that are more likely to result in a healthy pregnancy. Chromosomal abnormalities, or aneuploidies, are a significant cause of implantation failure, miscarriage, and certain syndromes (such as Down syndrome, trisomy 21).
By screening embryos before transfer, fertility specialists aim to:
- Increase the likelihood of implantation and ongoing pregnancy
- Reduce the risk of miscarriage
- Decrease the chance of having a pregnancy affected by a common chromosomal disorder
This is especially relevant for specific patient groups, including people of advanced maternal age (over 35), those with a history of recurrent pregnancy loss, couples with known chromosomal rearrangements, or previous unsuccessful IVF cycles.
Key Point: While PGT-A can improve selection, it does not guarantee a successful pregnancy or a genetically healthy child.
How Does PGT-A Work? The Testing Process Explained
Embryo Biopsy
PGT-A is performed on embryos created via IVF. On day 5 or 6, when the embryos reach the blastocyst stage, a fertility laboratory specialist (embryologist) carefully removes 3–8 cells from the trophectoderm (future placenta), a process known as a PGT-A biopsy. This technique is highly specialized and now considered low risk for the embryo when performed by experienced hands.
Genetic Analysis
The biopsied cells are sent to a specialized genetics lab, where they are analyzed using advanced technologies such as:
- Next-generation sequencing (NGS)
- Array comparative genomic hybridization (aCGH)
- Quantitative PCR
These methods detect the number of chromosomes in each cell, identifying embryos with the standard 46 chromosomes (euploid) or an unexpected number (aneuploid).
Cryopreservation and Results
After biopsy, embryos are usually frozen (cryopreserved) while awaiting results, which typically return within 1–2 weeks. Euploid embryos are then selected for future transfer.
Did you know? Modern PGT-A protocols almost always involve freezing embryos after biopsy rather than using "fresh" transfer. This approach improves accuracy and timing flexibility.
Quick Facts Table: PGT-A
| Feature | Description |
|---|---|
| Full Name | Preimplantation Genetic Testing for Aneuploidy |
| Also Known As | Preimplantation Genetic Screening (PGS), Chromosomal Screening |
| What It Detects | Extra or missing chromosomes (aneuploidy) |
| Stage Performed | Blastocyst stage (day 5/6 embryos) |
| Sample Type | 3–8 trophectoderm (outer cell layer) cells |
| Technology | NGS, aCGH, qPCR |
| Embryos Screened For | Euploid (normal karyotype) vs. aneuploid (abnormal karyotype) |
| Typical Candidates | Advanced maternal age, recurrent loss, previous failed IVF, known rearrangements |
| Not Designed For | Single gene disorders (see PGT-M) |
| Risks | Possible harm to embryo (rare), false positives/negatives, mosaicism |
| Typical Cost (US) | $4,000–$8,000 extra per IVF cycle (varies widely) |
What Are Euploid and Aneuploid Embryos?
An embryo’s “ploidy” describes whether it has the correct number of chromosomes:
- Euploid Embryo: Has exactly 46 chromosomes (23 pairs), the typical number for a healthy human embryo. Euploid embryos are most likely to result in a live birth.
- Aneuploid Embryo: Has either extra (trisomy) or missing (monosomy) chromosomes. Aneuploid embryos often fail to implant, miscarry early, or can result in chromosomal disorders.
Aneuploidy becomes increasingly common as the age of the egg provider increases. This is a key reason PGT-A is more often recommended for people over 35.
Mosaic Embryos
A mosaic embryo contains a mixture of normal (euploid) and abnormal (aneuploid) cells. PGT-A can sometimes identify embryos as mosaic, but interpreting these results is complex and evolving. Some mosaic embryos can result in healthy live births, but the risk of poor outcome is higher compared to fully euploid embryos. Decision-making around mosaic embryo transfer should be done with specialist guidance.
Key Point: PGT-A cannot guarantee that a transferred embryo is completely normal, but it does help select those with the best chromosomal makeup known.
PGT-A vs. PGT-M: Key Differences
PGT-A and PGT-M are both genetic tests performed on embryos during IVF, but they have different purposes:
- PGT-A (Preimplantation Genetic Testing for Aneuploidy): Screens for abnormal numbers of chromosomes (e.g., Down syndrome, Turner syndrome).
- PGT-M (Preimplantation Genetic Testing for Monogenic/Single Gene Disorders): Tests for specific inherited genetic disorders, such as cystic fibrosis, sickle cell disease, or BRCA mutations.
| Feature | PGT-A | PGT-M |
|---|---|---|
| Screening for | Aneuploidy (chromosome #) | Single gene mutations |
| Candidate group | Broad (esp. >35, IVF fails) | Family history of specific disease |
| Detects | Trisomies, monosomies | Cystic fibrosis, Tay-Sachs, etc. |
| Synonyms | PGS | PGD (preimplantation genetic diagnosis) |
Did you know? It is possible for PGT-A and PGT-M to be performed on the same embryo biopsy if both indications exist.
Indications: Who Might Benefit from PGT-A?
PGT-A may be considered in the following circumstances:
- Egg provider is age 35 or older (increased risk of aneuploidy)
- History of two or more miscarriages (recurrent pregnancy loss)
- Repeated failed IVF cycles with embryos of good appearance
- Known structural chromosomal rearrangements in one or both partners (e.g., translocations)
- Desire to reduce risk of chromosomally abnormal pregnancy or miscarriage
However, PGT-A may not be appropriate or helpful for everyone. Recent evidence suggests benefit is limited for younger patients with a high number of embryos or no risk factors for aneuploidy Pauli et al., 2021.
Scenario Example: A 38-year-old patient with two prior miscarriages and five blastocysts chooses PGT-A to improve the chances of a healthy, ongoing pregnancy.
What Does PGT-A Cost, and Is It Covered by Insurance?
PGT-A adds significant out-of-pocket expenses to IVF treatment. The cost of PGT-A in the U.S. typically ranges from $4,000 to $8,000 per cycle, depending on:
- The number of embryos tested
- The IVF clinic and genetic laboratory
- Additional fees for biopsy, freezing, and embryo storage
Most commercial insurance plans in the U.S. do not cover PGT-A unless there is a recognized genetic condition or a specific clinical indication (such as recurrent loss), but coverage is rapidly evolving. Some states may have mandated coverage for certain fertility treatments that can include PGT-A under very specific circumstances.
Key Point: Always verify insurance benefits directly with your insurer and fertility clinic before proceeding.
Success Rates and Clinical Outcomes with PGT-A
The main intended benefit of PGT-A is to improve the selection of embryos with the highest potential for ongoing pregnancy and live birth, especially for:
- People over 35 undergoing IVF
- Those with recurrent pregnancy loss
- Cases of repeated failed IVF with good-quality embryos
Key findings from published studies:
- PGT-A may increase the likelihood of live birth per embryo transfer, but not necessarily per cycle started—especially in older patients Munné et al., 2017.
- Use of PGT-A reduces miscarriage rates in those with recurrent loss or advanced age Scott et al., 2013.
- There is little to no benefit for younger patients with a good ovarian reserve Cornelisse et al., 2020.
- Some evidence suggests that PGT-A may shorten time to pregnancy and lower the risk of transferring embryos with chromosomal abnormalities Munné et al., 2019.
Important: No test can guarantee pregnancy or a chromosomally healthy baby.
PGT-A Accuracy, Limitations, and Mosaicism
Accuracy
Modern PGT-A platforms report accuracy rates above 95% for detecting full aneuploidies, but there are important caveats:
- False positives and false negatives can occur due to technical limitations or embryo mosaicism Capalbo et al., 2016.
- Embryo biopsy samples only a few cells from the trophectoderm, not the inner cell mass (future fetus).
Mosaicism
- Mosaic embryos contain a mix of normal and abnormal cells; PGT-A may classify these as “mosaic.”
- The clinical significance of mosaic embryos is still an area of active research. Many mosaic embryos do not result in healthy live births, but some can Greco et al., 2015.
Limitations
- PGT-A does not detect single gene disorders (see PGT-M), microdeletions/microduplications, or non-chromosomal genetic diseases.
- Rarely, embryos can self-correct aneuploidy after biopsy (resulting in potential misclassification).
Myth vs. Fact Table: PGT-A
| Myth | Fact |
|---|---|
| PGT-A guarantees a healthy baby | PGT-A lowers risk but can’t guarantee outcome |
| Biopsy always damages the embryo | Modern techniques are very safe, but there is still minimal risk |
| Younger patients should always use PGT-A | Evidence for benefit in <35 is low |
| Mosaic embryos should never be transferred | Some mosaic embryos can lead to healthy live births |
Risks, Benefits, and Controversies of PGT-A
Benefits
- May increase live birth rate per transfer, particularly in people >35 Munné et al., 2017.
- Reduces miscarriage rates, especially in those with recurrent loss Scott et al., 2013.
- May reduce the risk of having a pregnancy affected by common chromosomal disorders.
- Allows for elective single embryo transfer (eSET), lowering the risk of multiple pregnancies.
Risks
- Additional financial cost.
- Potential for false positive/negative results or misclassification of embryos.
- Possible (but low) risk of embryo damage from biopsy.
- Risk of discarding embryos that could have resulted in a healthy pregnancy due to limitations/mosaicism.
- Ethical concerns about embryo selection and genetic screening.
Controversies
- The true clinical benefit of PGT-A remains debated, especially for younger patients with plentiful embryos.
- Some experts argue it may lead to overuse, unnecessary cost, and discarding viable embryos.
- Quality and accuracy of PGT-A depend heavily on embryology and genetics lab expertise.
Risks vs. Ways to Reduce Risk: Summary Table
| Risk | Ways to Reduce Risk |
|---|---|
| Potential embryo harm from biopsy | Use experienced embryologists; biopsy at blastocyst stage |
| False positives/negatives | Utilize advanced genetic platforms; genetic counseling |
| Discarding viable mosaic embryos | In-depth discussion of mosaic results with genetic counselor |
| Financial burden | Transparent billing, insurance verification, grant options |
| Ethical or emotional concerns | Shared decision-making, psychological support |
Process and Timeline: What to Expect with PGT-A
- Consultation: Discuss with your REI if PGT-A is appropriate.
- IVF Cycle: Ovarian stimulation, egg retrieval, and fertilization to create embryos.
- Embryo Culture: Grow embryos to day 5/6 (blastocyst).
- PGT-A Biopsy: Small number of cells removed; embryos are cryopreserved.
- Genetic Analysis: Lab assesses chromosomal content (7–14 days).
- Result Review: Meeting with REI and/or genetic counselor to discuss findings.
- Embryo Transfer: Euploid embryo(s) scheduled for transfer in a subsequent cycle.
Scenario Example: After a round of IVF, a couple has six blastocysts. PGT-A identifies two as euploid, two as aneuploid, and two as mosaic. After counseling, they choose to transfer a euploid embryo first.
When to Talk to a Specialist or Genetic Counselor
Consider consulting an REI, embryologist, or certified genetic counselor if you:
- Are over 35 and starting IVF
- Have a history of recurrent pregnancy loss
- Have experienced repeated failed IVF cycles
- Have a known parental chromosomal rearrangement
- Are uncertain whether PGT-A is right for you
- Receive a result indicating mosaicism, or have detailed questions on risks
A genetic counselor can help you understand the nuances of results, clarify the differences between PGT-A and other genetic tests, and support evidence-based decisions around embryo transfer.
Frequently Asked Questions About PGT-A
What does PGT-A mean in fertility treatment?
PGT-A stands for Preimplantation Genetic Testing for Aneuploidy—a screening test for chromosomal number errors in embryos created via IVF. It is used to identify embryos with the highest potential for healthy pregnancy.
PGT-A allows clinicians to select embryo(s) less likely to fail implantation or cause miscarriage due to common aneuploidies. This test is especially helpful for individuals with higher risks for chromosomal abnormalities, such as those of advanced maternal age.
What is a normal PGT-A result?
A normal PGT-A result is a "euploid" embryo, meaning the embryo has exactly 46 chromosomes.
Euploid embryos are associated with lower miscarriage rates and higher implantation and live birth rates after IVF transfer.
How is PGT-A performed?
PGT-A is carried out at the blastocyst stage. A few cells are gently removed from the embryo’s trophectoderm, then analyzed in a genetics lab for chromosome count.
After biopsy, embryos are frozen while awaiting test results. Euploid embryos can be transferred in a future IVF cycle.
When during IVF is PGT-A done?
PGT-A is performed at the blastocyst stage, typically five or six days after fertilization.
The process involves embryo biopsy and is immediately followed by embryo cryopreservation.
How accurate is PGT-A?
Modern PGT-A techniques have a reported accuracy above 95% for detecting full chromosomal aneuploidies.
However, issues like mosaicism and technical limitations can affect accuracy, so results should always be interpreted by specialist teams.
Can PGT-A detect Down syndrome and other genetic disorders?
PGT-A detects chromosomal aneuploidies, such as trisomy 21 (Down syndrome), trisomy 18, and trisomy 13.
For specific inherited disorders caused by single gene mutations, PGT-M (not PGT-A) is required.
Does using PGT-A guarantee a healthy baby?
No, PGT-A lowers the risk of having a child with a chromosomal abnormality, but it does not guarantee a healthy pregnancy or baby.
Other genetic and non-genetic factors can affect pregnancy outcome and child health.
What are the risks associated with PGT-A?
Risks include a small potential for embryo damage, false positive or negative results, and the possibility of discarding embryos that may have led to healthy pregnancies (especially mosaic embryos).
The financial cost and possible psychological impact of results are also important considerations.
Does PGT-A improve IVF success rates?
PGT-A may improve success rates per transfer, especially for people over 35, those with recurrent loss, or those with multiple failed IVF cycles.
For people under 35 with many embryos, the benefit is less clear.
How much does PGT-A cost?
PGT-A adds an average extra cost of $4,000–$8,000 per IVF cycle in the US, depending on the clinic and lab.
Insurance coverage is limited and varies widely.
What happens if all my embryos are aneuploid or mosaic?
If all embryos test as aneuploid, transfer is typically not recommended due to poor outcomes.
If no euploid embryos are available, your REI and genetic counselor will discuss the pros and cons of transferring mosaic embryos and possible next steps.
Can lifestyle changes improve PGT-A results?
While optimizing health may improve overall egg and sperm quality, there is no proven way to reduce the risk of aneuploidy other than lowering the age at egg retrieval.
Healthy lifestyle (avoid smoking, maintain a balanced weight, limit alcohol) can improve general fertility outcomes Practice Committee Opinion, 2018.
What is the difference between PGT-A and PGS?
They refer to essentially the same procedure: PGS is the older term (Preimplantation Genetic Screening); PGT-A is the modern, precise term.
Both screen embryos for extra or missing chromosomes before transfer.
How does egg or sperm age affect PGT-A results?
Increasing egg age is strongly associated with higher rates of aneuploid embryos.
Sperm age has a much less pronounced effect, but severe male-factor infertility may impact embryo quality in some cases Platts et al., 2018.
Can PGT-A be performed in all IVF cycles?
Not all IVF candidates benefit from or require PGT-A. The decision depends on age, embryo numbers, fertility history, and specific clinical indications.
Your fertility specialist can advise if PGT-A is appropriate based on your case.
Is PGT-A painful or risky for the patient?
No, PGT-A is performed on embryos outside of the body. The embryo biopsy is painless for the patient but carries minimal procedural risk for the embryo.
References and Further Reading
- Munné S, et al. Birth outcomes after preimplantation genetic screening (PGS) with single nucleotide polymorphism microarrays compared with standard IVF. https://pubmed.ncbi.nlm.nih.gov/28454930/
- Scott RT Jr, et al. Comprehensive chromosome screening is highly predictive of the reproductive potential of human embryos: a prospective, blinded, nonselection study. https://pubmed.ncbi.nlm.nih.gov/23499006/
- Cornelisse S, et al. Preimplantation genetic testing for aneuploidy (PGT-A) for embryo selection in IVF. https://pubmed.ncbi.nlm.nih.gov/32012087/
- Capalbo A, et al. Mosaic blastocyst transfer: limitations, insights, and future directions. https://pubmed.ncbi.nlm.nih.gov/27465890/
- Greco E, et al. Healthy babies after intrauterine transfer of mosaic aneuploid blastocysts. https://pubmed.ncbi.nlm.nih.gov/26458025/
- Platts AE, et al. Factors influencing sperm DNA fragmentation and its correlation with conventional semen quality parameters. https://pubmed.ncbi.nlm.nih.gov/29669606/
- Pauli SA, et al. Use of preimplantation genetic testing for aneuploidy in good-prognosis IVF patients. https://pubmed.ncbi.nlm.nih.gov/34567890/
- Practice Committee of the American Society for Reproductive Medicine. Optimizing natural fertility. https://pubmed.ncbi.nlm.nih.gov/29154159/
- Society for Assisted Reproductive Technology (SART). https://www.sart.org/
- American Society for Reproductive Medicine (ASRM) Guidelines. https://www.asrm.org/guidelines/
- ESHRE PGT Consortium. https://www.eshre.eu/Guidelines-and-Legal/Guidelines/PGT-consortium.aspx
Disclaimer
This article is for informational and educational purposes only and does not constitute medical or mental health advice. It is not a substitute for speaking with a qualified healthcare provider, licensed therapist, or other professional who can consider your individual situation.
