What Is Preimplantation Genetic Testing (PGT)?
Preimplantation Genetic Testing (PGT) is a specialised test that examines genetic material from embryos created through in vitro fertilisation (IVF). It can help identify certain chromosomal abnormalities or specific genetic conditions before an embryo is transferred to the uterus.
PGT involves collecting a small sample of cells from an embryo and analysing them in a laboratory. Depending on the type of test performed, it may provide information about chromosome number or the presence of a particular inherited genetic condition.
PGT can help fertility specialists and patients make informed decisions during IVF treatment. However, it cannot detect every genetic condition, guarantee a healthy baby, or ensure a successful pregnancy.
What Is the Difference Between PGT and PGD?
Preimplantation Genetic Testing (PGT) is the current umbrella term for genetic testing performed on embryos before implantation. The older term Preimplantation Genetic Diagnosis (PGD) was commonly used for testing embryos for a specific inherited genetic disorder.
Today, the type of PGT recommended depends on the genetic concern being investigated and the patient’s medical history.
The three main categories are:
- PGT-A (Preimplantation Genetic Testing for Aneuploidy): Examines the number of chromosomes in an embryo.
- PGT-M (Preimplantation Genetic Testing for Monogenic Disorders): Tests for a specific inherited condition caused by a change in a single gene.
- PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements): Evaluates embryos for certain chromosome abnormalities associated with structural rearrangements in a parent’s chromosomes.
These tests serve different purposes, and not every person undergoing IVF needs genetic testing.
What Is PGT-A?
Preimplantation Genetic Testing for Aneuploidy (PGT-A) evaluates whether an embryo has an abnormal number of chromosomes.
Typically, human cells contain 46 chromosomes arranged in 23 pairs. An embryo with an extra or missing chromosome may have a chromosomal abnormality that affects its development or the likelihood of a successful pregnancy.
PGT-A is generally performed on a small sample of cells from a blastocyst-stage embryo, usually developed over approximately five to seven days after fertilisation. The sample is sent for laboratory analysis, while the embryo is commonly frozen until the results are available and a suitable transfer plan can be made.
PGT-A may identify embryos with chromosome patterns associated with conditions such as Down syndrome, which is commonly associated with an extra copy of chromosome 21. However, PGT-A is a screening test rather than a definitive diagnosis, and it does not assess every genetic condition.
Results can sometimes be inconclusive or indicate mosaicism, in which different cells may have different chromosome patterns. Genetic counselling and, where appropriate, confirmatory prenatal testing may be discussed.
Who Should Consider PGT-A?
PGT-A is not compulsory for every IVF cycle. A fertility specialist may discuss it based on the patient’s reproductive history, treatment goals, and clinical circumstances.
It may be considered in situations such as:
- Advanced maternal age: The likelihood of embryos having certain chromosome abnormalities increases with maternal age.
- Repeated pregnancy loss: PGT-A may be discussed in selected cases, although it has not been shown to improve outcomes for every patient with recurrent miscarriage.
- Previous unsuccessful IVF cycles: The specialist may evaluate whether PGT-A is likely to provide useful information in the context of previous treatment outcomes.
- Previous pregnancy involving a chromosomal abnormality: Further assessment may help determine which genetic test, if any, is appropriate.
- Individualised fertility planning: Some patients may consider PGT-A after discussing its potential benefits, limitations, costs, and alternatives.
A family history of an inherited genetic disorder may call for PGT-M or another targeted test rather than PGT-A. The appropriate test depends on the specific genetic concern.
What Is the PGT Procedure?
The process generally involves several stages as part of an IVF treatment cycle.
1. Ovarian stimulation and egg collection
Medication is used to stimulate the ovaries to develop eggs. The eggs are collected through a medical procedure and fertilised in the laboratory, often using conventional IVF or intracytoplasmic sperm injection (ICSI), depending on the treatment plan.
2. Embryo development
The fertilised eggs are monitored as they develop. Embryos that reach the blastocyst stage may be considered for biopsy if genetic testing is planned.
3. Embryo biopsy
A trained embryologist collects a small sample of cells from the embryo’s outer cell layer. The procedure requires specialised laboratory equipment and careful handling.
4. Genetic analysis
The sample is sent for genetic analysis according to the type of PGT being performed. The laboratory examines the sample for the chromosome or genetic changes relevant to the test.
5. Embryo transfer planning
The results are reviewed by the fertility team. An embryo may be considered for transfer based on the findings, its developmental assessment, and the patient’s individual treatment plan. Embryos are commonly frozen while awaiting results.
PGT does not guarantee that an embryo will implant or result in a live birth. The procedure also cannot eliminate all risks of genetic or developmental conditions.
What Are the Potential Benefits of PGT?
Depending on the type of testing and the patient’s circumstances, PGT may offer several potential benefits:
- Additional genetic information: Provides information about specific chromosome abnormalities or inherited genetic conditions.
- Support for embryo selection: May help the fertility team and patient make decisions about which embryos to consider for transfer.
- Risk assessment for certain inherited conditions: PGT-M can help identify embryos affected by a specific genetic disorder when the relevant genetic change is known.
- Informed fertility planning: Results may help guide discussions about embryo transfer and further testing during pregnancy.
The benefits vary by test type and individual circumstances. PGT-A may reduce the likelihood of transferring an embryo with certain chromosome abnormalities, but it does not consistently improve the overall chance of having a baby for every patient undergoing IVF. It may also reduce the number of embryos considered suitable for transfer.
Does PGT Prevent Miscarriage or Guarantee IVF Success?
No. Some chromosome abnormalities are associated with miscarriage, and PGT may provide useful information in selected cases. However, it cannot prevent every miscarriage or guarantee a successful IVF outcome.
PGT results are based on a sample of cells and may not perfectly represent every cell in the embryo. False-positive, false-negative, mosaic, or inconclusive results are possible. Genetic testing also cannot rule out every birth defect or inherited condition.
Your fertility specialist can explain what the results mean, the limitations of the selected test, and whether prenatal screening or diagnostic testing should be considered if pregnancy occurs.
PGT at Jyoti IVF
At Jyoti IVF, patients can discuss genetic testing options as part of their fertility treatment planning. If PGT is being considered, the fertility team can help explain the differences between PGT-A, PGT-M, and PGT-SR, and whether a particular test may be relevant to your medical history.
The decision to use PGT should be based on individual clinical needs, appropriate genetic counselling, and an understanding of the potential benefits and limitations.
Considering IVF with genetic testing? Consult Jyoti IVF to discuss your fertility goals and explore suitable treatment options with a qualified specialist.
Medical disclaimer: This article is for general informational purposes and does not replace professional medical advice or genetic counselling. PGT availability and suitability vary by clinic and patient. Confirm the availability of these services with Jyoti IVF and discuss the limitations and alternatives with your treating clinician.