Preimplantation Genetic Testing (PGT)
Assisted reproduction has revolutionized couples’ ability to have children, even when facing fertility problems. One of the most innovative tools in this process is preimplantation genetic testing (PGT). PGT can identify embryos with particular genetic or chromosomal findings before transfer; it cannot guarantee an unaffected pregnancy or child. In this article, we look in detail at preimplantation genetic testing, its types, how it works, what the benefits are, and who can benefit from it.
Types of Preimplantation Genetic Testing (PGT)
There are different types of PGT, each used for different purposes:
- PGT-A (Aneuploidy): Tests for aneuploidies, i.e., abnormalities in chromosome number, such as Down syndrome.
- PGT-M (Monogenic): Tests for specific monogenic disorders, such as cystic fibrosis and beta-thalassemia.
- PGT-SR (Structural Rearrangements): Tests for structural chromosome rearrangements, such as translocations and inversions. These rearrangements, usually carried by one of the two parents, may be associated with infertility, recurrent miscarriage, and the birth of children with health problems.
How does Preimplantation Genetic Testing work?
The PGT procedure includes several stages:
- In Vitro Fertilisation (IVF): The woman receives medications to stimulate her ovaries to produce multiple eggs. These eggs are collected and fertilised with her partner’s sperm (or donor sperm) in the laboratory.
- Embryo Culture: The fertilised eggs (embryos) are cultured for several days in the laboratory, usually until the blastocyst stage (day 5 or 6 of culture).
- Embryo Biopsy: At this stage, a few cells are removed from the embryo for genetic analysis. This biopsy is generally considered not to harm embryo development.
- Genetic Analysis: The removed cells are analysed to detect genetic abnormalities.
- Selection and Embryo Transfer: Embryos that do not appear to have genetic abnormalities are selected for transfer to the woman’s uterus. Embryo transfer is performed in a natural or slightly stimulated cycle to increase the chances of success.
When may PGT be considered?
PGT can be particularly useful for the following couples:
- Couples with Family History of Genetic Disorders: If one or both parents are carriers of a genetic disorder (e.g., carriers of beta-thalassemia or cystic fibrosis), PGT can help avoid transmitting the disorder to their children.
- Couples with Recurrent Miscarriages: Certain genetic abnormalities (e.g., structural chromosome rearrangements) can cause recurrent miscarriage. PGT can detect these problems before implantation.
- Couples with Multiple Implantation Failures: In cases where IVF has repeatedly failed, PGT can help identify healthy embryos that have greater chances of successful implantation.
- Women of Advanced Age: Women over 35 years have an increased risk of chromosomal abnormalities in their embryos. PGT can help identify and select healthy embryos.
What are the Benefits of Preimplantation Genetic Testing?
The use of PGT can offer significant benefits to prospective parents:
- Reduction of Risk of Genetic Diseases: By identifying embryos that appear unaffected, PGT reduces the risk of having a child with a genetic disease.
- Increased Chances of Successful Pregnancy per Embryo Transfer: By selecting healthy embryos for implantation, PGT can increase the chances of successful pregnancy and reduce the risk of miscarriage after each embryo transfer.
- Reduction of Repeated IVF Failures: By detecting the healthiest embryos, PGT can reduce the need for multiple IVF cycles, saving time, money, and emotional distress.
What are the Limitations and Challenges of Preimplantation Genetic Testing?
- Cost: The PGT procedure is often expensive. It is important to discuss the cost with your doctor and consider all your financial options.
- Ethical Issues: Some people have ethical objections to selecting embryos on the basis of their genetic characteristics. It is important to discuss these issues with your Fertility/Reproductive Medicine specialist and your geneticist.
- Legal Restrictions: Greek legislation sets certain restrictions on the use of this technology. Specifically, preimplantation genetic testing is permitted when there is an increased risk of transmitting genetic diseases to a couple’s children (e.g., both parents are carriers of beta-thalassemia) or an increased risk of miscarriages due to chromosomal abnormalities. It is also permitted for couples who have had recurrent (at least 2) miscarriages or failed (at least 3) embryo transfers. Finally, before preimplantation genetic testing can be performed, authorization from the National Authority for Medically Assisted Reproduction is required.
- Technical Limitations: PGT cannot detect all genetic abnormalities, and there is always the possibility of false negatives or false positives. This means that while PGT can reduce the risk of genetic disorders, it cannot eliminate it completely. Also, it can take a considerable time (two to six months) to develop a bespoke test for the specific genetic disease carried by one or both parents.
- IVF Success Rates: The success of IVF is not guaranteed and depends on many factors, including the woman’s age and general health. Thus, even in cases of preimplantation genetic testing, the probability of success usually does not exceed 60% per embryo transferred.
What are the Risks of Preimplantation Genetic Testing?
- Potential Embryo Damage: Embryo biopsy is an invasive procedure that, theoretically, can cause damage to the embryo. This, however, is rare, especially in accredited laboratories with experienced personnel.
- Implantation Failure: As mentioned above, even healthy embryos may not implant successfully in the uterus.
- Errors in Genetic Analysis: Although rare, there may be false positive or false negative results in genetic analysis. For this reason, prenatal diagnosis during pregnancy—using chorionic villus sampling or amniocentesis—is recommended to confirm the PGT result.
Conclusion
Preimplantation genetic testing is an important tool in modern reproductive medicine that can help many couples have healthy children. Despite ethical issues and technical challenges, PGT offers hope to couples with a family history of genetic disorders and increases the chances of successful pregnancy.
If you would like advice based on your circumstances, contact Dr Christos Venetis to arrange a consultation.