Preimplantation genetic testing (PGT): PGT-M, PGT-SR and PGT-A
Preimplantation genetic testing: the short answer
Preimplantation genetic testing (PGT) analyses a small sample of cells from an embryo created through IVF. The biopsy is usually taken when the embryo reaches the blastocyst stage, before a possible transfer. The embryo is generally cryopreserved while the laboratory analyses the sample.
PGT is not one single test. PGT-M looks for a known single-gene condition. PGT-SR looks for a known structural chromosome rearrangement. PGT-A assesses chromosome copy number, also called aneuploidy. Each test answers a different question, and none can guarantee implantation, pregnancy or live birth.
The ASRM committee opinion on PGT-A states that routine PGT-A for every IVF patient has not been shown to improve overall outcomes. The ESHRE PGT recommendations describe the need for careful patient selection, counselling and laboratory quality processes.
What do PGT-M, PGT-SR and PGT-A mean?
The names are easy to mix up. Their purposes are different:
- PGT-M: tests for a specific known condition caused by a change in one gene. The family’s genetic finding must be understood before the test is planned.
- PGT-SR: tests for the effects of a known structural chromosome rearrangement, such as a translocation or inversion, in a parent.
- PGT-A: assesses whether the tested cells show the expected number of chromosome copies. It does not test for every genetic or developmental condition.
The older term PGD is still used in some documents, but PGT is the broader current terminology. Ask the genetics and embryology teams which test is being proposed and what question it is intended to answer.
Who might discuss PGT?
PGT is most clearly discussed when there is a specific genetic question. Examples include a known familial single-gene condition, a parental chromosome rearrangement, or a need for genetic counselling after a relevant reproductive history.
Age, previous pregnancy loss or previous implantation outcomes may lead to a conversation about PGT-A. They do not make PGT-A an automatic or universal step. The decision also depends on whether there are embryos suitable for biopsy, what result would change the plan, the cost, the laboratory pathway and the alternatives.
PGT should be offered with genetic counselling and informed consent. A patient should know what may happen if the report shows a mosaic result, no result or no embryo considered suitable for the planned transfer.
How is PGT carried out?
PGT is part of an IVF pathway rather than a stand-alone blood test:
- The team confirms the genetic question and, for some PGT-M cases, prepares the family-specific laboratory work before treatment.
- Ovarian stimulation, egg retrieval and fertilisation are carried out according to the IVF plan.
- Embryos are cultured to the blastocyst stage when development allows.
- A small sample of cells is taken from the outer layer of the blastocyst. The inner cell mass is not the routine biopsy target.
- The embryo is usually vitrified while the sample is sent for analysis.
- The genetics and embryology teams explain the report and discuss whether a later frozen embryo transfer is appropriate.
The biopsy and testing process requires strict identification, transport and quality-control procedures. The ESHRE laboratory guidance describes traceability and quality management as part of safe IVF laboratory practice.
What can the result tell you — and what can it not tell you?
A PGT report is limited to the question and method used. Depending on the test, it may report a result consistent with the condition being tested, an aneuploid or euploid pattern, mosaicism, a segmental finding, or no interpretable result.
Mosaic results can be difficult to interpret because the biopsy samples a small part of the embryo. There can also be technical limits, contamination concerns, false-positive or false-negative results, and results that cannot be classified with confidence. A result described as suitable for transfer is not a guarantee of implantation, pregnancy or a healthy child.
PGT does not replace prenatal care. The appropriate pregnancy tests and scans should still be discussed with the obstetric team.
PGT and sex selection
PGT should not be presented as a way to choose a preferred sex. The clinical and legal framework depends on the medical indication and the country where care is provided. In Turkey, ask the licensed centre and the genetics team to explain the current rules before making decisions about testing.
Dr. Aksoy’s approach
I start with the genetic question, not with the name of the test. What condition are we trying to identify? What would change if the report were positive, mosaic or inconclusive? If those questions are not clear, ordering a test can add cost and uncertainty without adding a useful decision.
PGT-A in particular should be discussed as one option within an IVF plan, not as a default quality label for every embryo. The ASRM evidence review supports that distinction.
Frequently asked questions
What is preimplantation genetic testing?
PGT analyses a small sample of cells from an IVF embryo, usually after it reaches the blastocyst stage, before a possible embryo transfer. It answers a defined genetic question; it does not test for every condition or guarantee a pregnancy.
What is the difference between PGT-M, PGT-SR and PGT-A?
PGT-M looks for a known single-gene condition, PGT-SR looks for a known structural chromosome rearrangement, and PGT-A assesses chromosome copy number. They are not interchangeable tests.
Does PGT guarantee a healthy baby?
No. A result is limited by the condition tested, the sample, the laboratory method and the possibility of mosaicism or no result. Prenatal care and the tests recommended during pregnancy remain important.
Who might discuss PGT?
Discussion may be appropriate when a family or parental genetic finding creates a specific testing question, or when the clinical history makes a targeted conversation useful. PGT-A is not a routine screening test for every IVF patient.
What happens after embryo biopsy?
The biopsied embryo is usually cryopreserved while the laboratory analyses the sample. The team then explains the report, including any mosaic, no-result or uncertain findings, before a transfer decision is made.
Important information
This page is for general education and does not replace genetic counselling or an individual fertility assessment. The indication for PGT, the laboratory method, the interpretation of a report and the decision to transfer an embryo must be discussed with the responsible medical and genetics teams.
Sources
- ASRM: The use of preimplantation genetic testing for aneuploidy
- ESHRE: Good practice recommendations for PGT
- ESHRE: Good practice in IVF laboratories
- Ankara Etlik City Hospital: PGT information
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