Preimplantation Genetic Testing (PGT) is a laboratory technique used during an IVF cycle to examine embryos for specific genetic or chromosomal abnormalities before embryo transfer. It can provide valuable information that helps fertility specialists and couples make more informed decisions when selecting embryos for transfer.
The terms PGD (Preimplantation Genetic Diagnosis) and PGS (Preimplantation Genetic Screening) were widely used in the past. Today, these techniques are generally described under the broader term Preimplantation Genetic Testing (PGT), which includes PGT-M for certain single-gene disorders, PGT-A for chromosomal abnormalities involving the number of chromosomes, and PGT-SR for specific structural chromosomal rearrangements.
PGT may be considered in selected IVF cases, particularly when there is a known risk of transmitting an inherited condition or when chromosomal factors may affect reproductive outcomes.
The decision to perform preimplantation genetic testing should always be based on the couple’s medical and family history, the type of genetic risk involved and an individualized assessment by the fertility specialist.
What Is Preimplantation Genetic Testing (PGT)?
Preimplantation Genetic Testing (PGT) is a group of genetic tests performed on embryos created through IVF before they are transferred to the uterus. Its purpose is to identify specific genetic or chromosomal abnormalities that may be present in an embryo.
During an IVF cycle, the embryos are cultured in the laboratory until they usually reach the blastocyst stage. At this point, a small number of cells can be carefully removed from the outer layer of the embryo and sent for genetic analysis. The embryo is typically vitrified while the laboratory results are being processed.
PGT is not a single test. Different types of testing are used depending on the medical indication. PGT-A evaluates the number of chromosomes, PGT-M is used when there is a known risk of a specific single-gene disorder, while PGT-SR may be recommended in cases involving certain structural chromosomal rearrangements.
The results of PGT can provide additional information before embryo transfer, but they do not guarantee implantation, pregnancy or the birth of a healthy baby.
PGD, PGS and PGT: What Is the Difference?
The terms PGD and PGS were commonly used in the past to describe different forms of genetic testing performed on embryos before embryo transfer. Today, these techniques are generally included under the broader term Preimplantation Genetic Testing (PGT).
PGD – Now Known Mainly as PGT-M
Preimplantation Genetic Diagnosis (PGD) was traditionally used when there was a known risk of passing a specific inherited disorder from the parents to the child. Today, this type of testing is mainly referred to as PGT-M, meaning Preimplantation Genetic Testing for Monogenic Disorders.
PGT-M may be used when one or both parents are known carriers of a specific genetic condition, such as cystic fibrosis or sickle cell disease.
PGS – Now Known as PGT-A
Preimplantation Genetic Screening (PGS) is the older term for what is now generally called PGT-A, or Preimplantation Genetic Testing for Aneuploidy.
PGT-A evaluates whether an embryo has the expected number of chromosomes. Abnormal chromosome numbers may be associated with implantation failure, miscarriage or certain chromosomal conditions.
What Is PGT-SR?
PGT-SR stands for Preimplantation Genetic Testing for Structural Rearrangements. It may be considered when one parent carries a known structural chromosomal rearrangement, such as a balanced translocation.
The appropriate type of PGT depends on the couple’s genetic background, medical history and the specific reason for testing.
Who May Be a Candidate for PGT?
Preimplantation Genetic Testing is not necessary for every IVF cycle. It may be considered in selected cases where there is a known genetic risk or a clinical reason to obtain additional information about the embryos before transfer.
Candidates for PGT-M
PGT-M may be considered when one or both parents carry a known single-gene disorder that could be inherited by their child. This includes certain hereditary conditions such as cystic fibrosis, sickle cell disease and some sex-linked genetic disorders.
Candidates for PGT-SR
PGT-SR may be recommended when one of the partners carries a structural chromosomal rearrangement, such as a balanced translocation or inversion. These changes may increase the risk of embryos having an unbalanced chromosome arrangement.
Candidates for PGT-A
PGT-A may be discussed in selected IVF cases, including:
- women of advanced maternal age,
- couples with a history of recurrent pregnancy loss,
- couples with previous unsuccessful IVF attempts,
- cases where chromosomal abnormalities are considered a possible contributing factor.
Whether PGT is appropriate should always be decided after an individualized fertility and genetic assessment. The type of testing recommended depends on the couple’s reproductive history, age, genetic background and the specific clinical indication.
How Is Preimplantation Genetic Testing Performed?
Preimplantation Genetic Testing is carried out as part of an IVF cycle and involves several carefully coordinated laboratory steps.
First, the ovaries are stimulated and the eggs are collected through the standard IVF procedure. The eggs are then fertilized in the laboratory, and the resulting embryos are cultured for several days until they usually reach the blastocyst stage.
At this stage, a small number of cells are removed from the outer layer of each suitable embryo through a procedure known as embryo biopsy. These cells are sent to a specialized genetic laboratory for analysis, while the embryos are usually frozen using vitrification.
The genetic analysis performed depends on the type of PGT required. It may assess chromosome number, specific single-gene disorders or structural chromosomal abnormalities.
Once the results are available, the fertility specialist reviews them together with the embryology team and the couple. An appropriate embryo may then be selected for transfer in a subsequent cycle.
The embryo is thawed, the endometrium is prepared and the embryo transfer is performed at the appropriate time.
What Can Preimplantation Genetic Testing Detect?
Preimplantation Genetic Testing can provide information about specific genetic or chromosomal abnormalities in embryos before embryo transfer. The type of abnormality that can be identified depends on the specific form of PGT being performed.
PGT-A
PGT-A assesses the number of chromosomes in an embryo. It can identify embryos with an abnormal number of chromosomes, a condition known as aneuploidy. These abnormalities may be associated with implantation failure, miscarriage or certain chromosomal conditions.
PGT-M
PGT-M is designed to test for a specific single-gene disorder when there is a known genetic risk within the family. It may be used for inherited conditions such as cystic fibrosis, sickle cell disease or other monogenic disorders.
PGT-SR
PGT-SR is used when one of the parents carries a known structural chromosomal rearrangement. It can help identify embryos that may have inherited an unbalanced chromosomal structure.
It is important to understand that PGT does not screen for every possible genetic condition. Each test is designed for a specific indication, and the results should always be interpreted together with the couple’s medical and genetic history.
Benefits and Limitations of Preimplantation Genetic Testing
Preimplantation Genetic Testing can provide important information about embryos before transfer, particularly in IVF cycles where there is a known genetic or chromosomal risk. However, it is important to understand both its potential benefits and its limitations.
Potential Benefits of PGT
Depending on the type of testing performed, PGT may help:
- identify embryos affected by specific inherited genetic disorders,
- detect certain chromosomal abnormalities,
- reduce the risk of transmitting a known genetic condition,
- provide additional information for embryo selection,
- support decision-making in selected IVF cases.
For couples with a known hereditary condition, PGT-M can be particularly valuable because it allows embryos to be tested for the specific disorder before embryo transfer.
Limitations of PGT
PGT does not guarantee implantation, pregnancy or the birth of a healthy baby. No genetic test can identify every possible condition, and results are limited to the abnormalities being investigated.
In some cases, the result may be inconclusive or may indicate mosaicism, where different cells within the embryo show different chromosomal patterns. It is also possible that no embryo suitable for transfer will be identified.
For these reasons, PGT should be recommended only after careful medical and genetic evaluation, with clear counselling about what the test can and cannot determine.
PGT and Embryo Transfer
After the genetic testing results are available, the fertility specialist and embryology team review the embryos and determine which may be considered suitable for transfer according to the type of PGT performed and the couple’s individual treatment plan.
Because embryos are commonly vitrified while the genetic analysis is being completed, embryo transfer usually takes place in a subsequent cycle. Before transfer, the selected embryo is carefully thawed and the endometrium is prepared to provide appropriate conditions for implantation.
Depending on the individual case, a single suitable embryo may be transferred to the uterus. The embryo transfer itself follows the standard IVF procedure and does not differ significantly because PGT has been performed.
It is important to remember that a favourable PGT result does not guarantee successful implantation or pregnancy. Several other factors, including embryo development, maternal age, endometrial conditions and individual fertility factors, can influence the outcome of an IVF cycle.
The decision regarding which embryo to transfer should therefore always be based on a complete clinical and embryological assessment.
Preimplantation Genetic Testing at Fertility Care
At Fertility Care, Preimplantation Genetic Testing is considered as part of an individualized IVF treatment plan when there is an appropriate medical or genetic indication.
Before recommending PGT, the fertility specialist carefully evaluates the couple’s medical and reproductive history, previous pregnancies or IVF attempts, family history of inherited conditions and any known genetic or chromosomal abnormalities.
Depending on the individual case, genetic counselling and additional testing may also be recommended before starting treatment. This helps determine which type of PGT — PGT-A, PGT-M or PGT-SR — is most appropriate and what information the test may provide.
The entire process, from ovarian stimulation and embryo development to biopsy, genetic analysis, vitrification and embryo transfer, is carefully coordinated according to each couple’s needs.
At Fertility Care, couples receive clear information about the potential benefits and limitations of preimplantation genetic testing so they can make an informed decision about their treatment.
Patients can arrange a consultation at our clinics in Athens or Tripoli to discuss whether PGT may be appropriate for their IVF journey.
Frequently Asked Questions About PGT
Is PGD the same as PGT?
PGD (Preimplantation Genetic Diagnosis) is an older term that has largely been replaced by Preimplantation Genetic Testing (PGT). Today, testing for a specific single-gene disorder is generally referred to as PGT-M.
Is PGS the same as PGT-A?
Yes. PGS (Preimplantation Genetic Screening) is the older term for what is now known as PGT-A – Preimplantation Genetic Testing for Aneuploidy. PGT-A assesses embryos for abnormalities in chromosome number.
Does PGT guarantee a successful pregnancy?
No. PGT can provide useful genetic or chromosomal information about an embryo, but it cannot guarantee implantation, pregnancy or the birth of a healthy baby. The outcome of IVF depends on several additional factors, including age and individual fertility circumstances.
When is the embryo biopsy performed?
Embryo biopsy for PGT is now commonly performed when the embryo has developed to the blastocyst stage, usually around day 5 or 6. A small number of cells are removed and sent for genetic analysis.
Can PGT detect all genetic diseases?
No. The information provided depends on the type of PGT performed. PGT-M targets specific known single-gene disorders, PGT-A evaluates chromosome number, and PGT-SR investigates chromosomal imbalances associated with structural rearrangements. The appropriate test is selected according to the individual genetic and medical indication.
