Preimplantation Genetic Testing: Types, Process, and Limits

It may be used to look for:

• abnormal chromosome numbers;
• a specific inherited genetic disorder;
• chromosome rearrangements;
• selected genetic risks known in a family.

The test helps provide information for embryo selection, but it cannot guarantee implantation, pregnancy, live birth, or the absence of all health conditions.

• preimplantation, meaning before an embryo implants in the uterus;
• genetic, meaning related to genes or chromosomes;
• testing, meaning laboratory examination.

Examples include:

• The couple chose preimplantation genetic testing during IVF.
• PGT was performed before embryo transfer.
• The embryos were frozen while the test results were processed.

Common expressions include:

• undergo PGT;
• PGT results;
• embryo biopsy;
• genetically tested embryo;
• PGT-A screening;
• PGT-M testing;
• chromosome testing;
• embryo selection.

The process commonly includes:

1. ovarian stimulation;
2. egg retrieval;
3. fertilization through IVF or ICSI;
4. embryo culture;
5. development to the blastocyst stage;
6. removal of a small number of cells;
7. freezing of the embryo;
8. genetic laboratory analysis;
9. review of the results;
10. possible frozen embryo transfer later.

The cells are generally taken from the trophectoderm, the outer layer of the blastocyst that later contributes mainly to the placenta.

The inner cell mass, which develops into the fetus, is usually not directly sampled.

PGT-A

PGT-A means preimplantation genetic testing for aneuploidy.

It examines whether an embryo appears to have the expected number of chromosomes.

Aneuploid embryos may have:

• an extra chromosome;
• a missing chromosome;
• another abnormal chromosome-number pattern.

PGT-A may be considered in some IVF situations, but it does not test for every genetic disease and does not guarantee pregnancy.

PGT-M

PGT-M means preimplantation genetic testing for monogenic disorders.

It is used when there is a known risk of a specific single-gene condition in a family.

Examples may include selected inherited disorders caused by changes in one gene.

The laboratory often needs genetic information from the intended parents and sometimes other relatives before treatment begins.

PGT-SR

PGT-SR means preimplantation genetic testing for structural rearrangements.

It may be used when a parent carries a chromosome rearrangement such as:

• a balanced translocation;
• certain inversions;
• another structural chromosome change.

The goal is to identify embryos more likely to have a balanced or appropriate chromosome arrangement.

At the blastocyst stage, an embryologist removes a small group of trophectoderm cells using specialized laboratory equipment.

The embryo is then usually vitrified.

Biopsy is a highly technical procedure. Most embryos tolerate it, but there is a small possibility of damage or failure to survive later warming.

Not every embryo develops far enough to be suitable for biopsy.

• euploid;
• aneuploid;
• mosaic;
• sometimes inconclusive.

A euploid result suggests the tested cells have the expected chromosome number.

An aneuploid result suggests an abnormal chromosome number.

A mosaic result means the sampled cells appear to contain a mixture of typical and atypical chromosome patterns.

These categories require careful interpretation because the biopsy samples only a small portion of the embryo.

A mosaic finding does not always mean that every cell in the embryo has the same chromosome pattern.

Depending on the specific result, some mosaic embryos may still be considered for transfer after counseling.

Decisions may involve:

• type of chromosome finding;
• degree of mosaicism reported;
• availability of other embryos;
• clinic policy;
• genetic counseling;
• reproductive goals.

A mosaic result should not be interpreted without specialist guidance.

It may not detect:

• every genetic disorder;
• all chromosome abnormalities;
• all forms of mosaicism;
• developmental disorders without a known genetic marker;
• conditions caused by environment or pregnancy complications;
• future diseases that are not part of the test.

False-positive, false-negative, or inconclusive results are possible.

PGT is therefore a risk-reduction and embryo-selection tool rather than a guarantee of genetic health.

Even after transfer of a tested embryo:

• implantation may fail;
• miscarriage may occur;
• an ectopic pregnancy is possible;
• pregnancy complications may develop.

A blood hCG test is still required after transfer.

Later ultrasound and ordinary prenatal care remain necessary.

During pregnancy, healthcare professionals may still discuss:

• ultrasound;
• cell-free DNA screening;
• chorionic villus sampling;
• amniocentesis;
• other prenatal tests.

This is especially important when PGT was performed for a known genetic condition or chromosome concern.

The appropriate follow-up depends on the PGT type and individual pregnancy.

• one or both partners carry a known genetic condition;
• a parent carries a chromosome rearrangement;
• there is a history of a specific inherited disorder;
• IVF is being performed and chromosome testing is being considered;
• repeated pregnancy loss has occurred in selected cases;
• previous pregnancies involved certain chromosome abnormalities.

Whether PGT-A improves outcomes for every IVF patient is more complex and depends on age, embryo number, treatment history, and clinical circumstances.

It should not automatically be assumed necessary for all IVF cycles.

PGT may therefore be discussed for selected people with recurrent pregnancy loss, especially when:

• a parental chromosome rearrangement is present;
• several IVF embryos are available;
• age-related chromosome abnormalities are a concern.

However, recurrent loss has many possible causes, and PGT cannot address uterine, hormonal, immune, or other non-genetic factors.

A complete medical evaluation remains important.

It identifies genetic or chromosomal information in embryos that already exist.

The test cannot:

• create healthier eggs;
• repair abnormal chromosomes;
• improve sperm DNA;
• guarantee implantation;
• increase the number of embryos available.

Because biopsy and testing require embryos, people with very few embryos may face difficult decisions about whether testing offers enough potential benefit.

When results become available, a selected embryo may later be thawed and transferred during a frozen embryo transfer cycle.

This separates:

• ovarian stimulation;
• egg retrieval;
• embryo biopsy;
• genetic testing;
• embryo transfer.

Modern vitrification allows embryos to remain stored while treatment decisions are made.

People may need to decide:

• which embryos to transfer;
• whether to transfer a mosaic embryo;
• what to do with embryos carrying a genetic condition;
• whether to continue storage;
• whether to donate or dispose of embryos where permitted;
• how much genetic information they want to know.

Different families may make different decisions based on medical advice, disability perspectives, religion, ethics, finances, and personalvalues.

Genetic counseling can help people understand the information without treating one decision as universally correct.

PGT repairs abnormal embryos.
No. It identifies findings but does not change the embryo.

Every IVF patient needs PGT.
No. Its usefulness depends on the individual situation.

A tested embryo always implants.
No. Implantation and pregnancy still depend on many factors.

PGT-A and PGT-M are the same test.
No. PGT-A examines chromosome number, while PGT-M targets a specific single-gene disorder.

PGT replaces prenatal testing.
Not always. Prenatal screening or diagnostic testing may still be recommended.

1. Preimplantation genetic testing examines cells from an IVF embryo before transfer.
2. The couple used PGT-M because of a known inherited disorder.
3. Can preimplantation genetic testing detect every genetic condition?
4. The embryo was frozen after the biopsy.
5. PGT-A may identify embryos with abnormal chromosome numbers.
6. A mosaic result may require genetic counseling before transfer.
7. PGT does not guarantee implantation or a healthy pregnancy.
8. Understanding preimplantation genetic testing helps readers distinguish embryo screening, genetic diagnosis, embryo transfer, and prenatal testing.

It allows intended parents to receive genetic information about embryos before transfer, but it also raises personal and ethical questions about reproductive choice, disability, embryo selection, and future parenthood.

Understanding PGT helps people make informed reproductive decisions while recognizing that genetic test results do not determine the value of a person, family, pregnancy, or child.