At a glance
Preimplantation genetic testing (PGT) involves embryo biopsy and genetic analysis, which carry specific risks such as embryo damage, mosaicism, and diagnostic inaccuracies. This guide explains these risks in plain language to help patients make informed decisions.
What Are the Risks of PGT?
Preimplantation genetic testing (PGT) is a technique used during IVF to screen embryos for genetic abnormalities before transfer. While it can provide valuable information, it is not without risks. Understanding these risks helps patients weigh the benefits against potential drawbacks. The main categories of risk include physical damage to the embryo during biopsy, inconclusive or mosaic results, and the possibility of false positives or false negatives. Each of these is explained below.
Embryo Biopsy: Potential for Damage
PGT requires removing a few cells from the embryo, typically from the trophectoderm (the outer layer that becomes the placenta) on day 5 or 6 of development. This biopsy is performed by a skilled embryologist using a laser or mechanical technique. While generally safe, there is a small risk of:
- Embryo damage: The biopsy procedure may occasionally harm the embryo, reducing its viability or ability to implant. Studies suggest the risk is low (around 1-2%) but varies by clinic and embryo quality.
- Reduced implantation potential: Some research indicates that biopsied embryos may have a slightly lower implantation rate compared to non-biopsied embryos, though this is debated and may depend on the embryo’s resilience.
- Embryo loss: In rare cases, the embryo may not survive the biopsy or the freezing-thawing process required for testing.
It is important to ask your clinic about their biopsy success rates and experience, as outcomes can vary.
Mosaic Results: What They Mean
A mosaic embryo contains a mixture of cells with normal chromosomes and cells with abnormal chromosomes. PGT can detect mosaicism, but interpreting these results is complex. Risks include:
- Uncertainty about embryo health: A mosaic result does not definitively indicate that the embryo is abnormal or will lead to a child with a genetic condition. Some mosaic embryos can self-correct or result in healthy births.
- Discarding potentially viable embryos: Patients may choose not to transfer a mosaic embryo, even though it might have developed into a healthy baby. Guidelines from professional societies suggest that mosaic embryos can be considered for transfer after counseling, but the decision is individual.
- Need for confirmatory testing: If a mosaic embryo is transferred and results in pregnancy, prenatal diagnosis (e.g., amniocentesis) is recommended to confirm the genetic status of the fetus.
Discuss with your clinic how they report mosaicism and what options are available for mosaic embryos.
False Positives and False Negatives
PGT is highly accurate but not perfect. Errors can occur due to technical limitations or biological factors.
- False positive: The test indicates an abnormality when the embryo is actually normal. This can lead to discarding a healthy embryo. False positives are more common with PGT-A (aneuploidy screening) for certain chromosomes or when mosaicism is present.
- False negative: The test reports a normal result when the embryo actually has a genetic abnormality. This could result in transferring an affected embryo. False negatives are rare but can happen if the biopsied cells do not represent the whole embryo (e.g., due to mosaicism) or if there is a technical error.
The accuracy of PGT depends on the laboratory’s quality control, the type of test (e.g., next-generation sequencing vs. array CGH), and the specific condition being tested. Ask your clinic about their validation data and error rates.
Other Considerations
- No guarantee of pregnancy or healthy baby: PGT cannot ensure implantation, a successful pregnancy, or a child free from all genetic conditions. It only screens for the specific abnormalities tested.
- Embryo attrition: Testing may reveal that many embryos are abnormal, reducing the number available for transfer. This can be emotionally and financially challenging.
- Cost and time: PGT adds expense and may require freezing embryos while waiting for results (typically 1-2 weeks). Not all clinics in Thailand offer the same turnaround times.
Questions to Ask Your Clinic
- What is your experience with embryo biopsy? How many biopsies have you performed?
- What is your embryo survival rate after biopsy?
- How do you report mosaic results? What are my options if an embryo is mosaic?
- What is the accuracy of your PGT method? What are your false positive and false negative rates?
- Do you offer genetic counseling to help interpret results?
Next Steps
- Research clinics in Thailand that offer PGT and compare their protocols.
- Schedule a consultation to discuss your specific situation and risk tolerance.
- Consider alternative options such as prenatal testing (e.g., NIPT, amniocentesis) if you are concerned about PGT risks.
For more information, see our PGT in Thailand overview, patient guides, and frequently asked questions.
Frequently asked questions
Can PGT damage the embryo?
Yes, there is a small risk of damage during the biopsy procedure, which may affect embryo viability. However, experienced clinics report low damage rates (around 1-2%). Discuss the clinic's biopsy success rates before proceeding.
What is a mosaic embryo result?
A mosaic result means the embryo has a mix of normal and abnormal cells. It does not necessarily mean the embryo is abnormal; some mosaic embryos can result in healthy births. Genetic counseling is recommended to understand the implications.
How accurate is PGT?
PGT is highly accurate but not 100%. False positives and false negatives can occur due to technical limitations or biological factors like mosaicism. Ask your clinic for their specific accuracy data.
Does PGT guarantee a healthy baby?
No. PGT only screens for the specific genetic conditions tested and cannot guarantee implantation, pregnancy, or a child free from all health issues.
What happens if all embryos are abnormal?
If no normal embryos are available for transfer, you may need to consider using donor eggs or sperm, or attempt another IVF cycle. Discuss all options with your clinic.
Continue your research
Medical information notice: This article is educational and does not replace individual assessment, diagnosis, genetic counselling or treatment advice from a licensed clinician. Provider services, availability, fees and policies should be verified directly before booking.
Need help turning research into a shortlist?
