Genetic Testing (PGT): Complete Guide to Preimplantation Genetic Testing

The technology feels almost futuristic: testing embryos for genetic conditions before they are even transferred to your uterus, potentially avoiding certain diseases or increasing the chances of a successful pregnancy. When your doctor mentions PGT, it can sound like a solution to uncertainty, a way to stack the odds in your favour.

But like most things in fertility treatment, the reality is more nuanced. Genetic testing of embryos offers genuine benefits in certain situations. It can also add cost, complexity, and new forms of uncertainty. Understanding what PGT can and cannot do helps you make an informed decision about whether it belongs in your treatment plan.

This guide explains the different types of genetic testing, who benefits most, what the process involves, and the limitations you should know about. Because this decision deserves clarity, not just hope.

What Is Preimplantation Genetic Testing?

Preimplantation genetic testing (PGT) refers to testing embryos created through IVF for genetic abnormalities before they are transferred to the uterus. The goal is to identify embryos that are genetically normal or free from specific conditions, improving the chances of a healthy pregnancy.

PGT can only be done with IVF because embryos must be created in the laboratory, biopsied, and tested before transfer. For an overview of IVF and other fertility treatment options, see our Treatments guide.

The Three Types of PGT

PGT-A (Aneuploidy): Tests for the correct number of chromosomes. Humans should have 46 chromosomes (23 pairs). Embryos with extra or missing chromosomes (aneuploidy) often fail to implant, miscarry, or result in conditions like Down syndrome.

PGT-M (Monogenic/Single Gene Disorders): Tests for specific inherited conditions caused by mutations in single genes, like cystic fibrosis, sickle cell disease, or Huntington's disease.

PGT-SR (Structural Rearrangements): Tests for chromosomal structural abnormalities like translocations, where pieces of chromosomes are rearranged. Parents with known translocations are at risk of passing along unbalanced genetic material.

PGT-A: Testing for Chromosome Number

PGT-A is the most commonly discussed form of genetic testing and the one most people are referring to when they talk about "genetic testing" of embryos.

What It Tests For

Every cell should have 46 chromosomes: 22 pairs of autosomes plus either XX (female) or XY (male). Aneuploidy means having the wrong number.

Common aneuploidies include:

• Trisomy 21 (Down syndrome): Three copies of chromosome 21
• Trisomy 18 (Edwards syndrome): Usually fatal
• Trisomy 13 (Patau syndrome): Usually fatal
• Monosomy X (Turner syndrome): Only one X chromosome
• Trisomy of other chromosomes: Usually result in failed implantation or early miscarriage

Most aneuploid embryos do not result in live births. They either fail to implant, miscarry early, or occasionally result in conditions that may or may not be compatible with life.

Who Benefits From PGT-A?

Advanced maternal age (38+): The rate of chromosomally abnormal eggs increases significantly with age due to age-related chromosomal issues. At 25, about 25% of embryos are aneuploid. At 40, it is closer to 70%. Testing allows selection of the euploid (normal) embryos.

Recurrent pregnancy loss: Women who have experienced multiple miscarriages may have a higher rate of aneuploid embryos. Testing can help identify normal embryos for transfer.

Repeated IVF failure: If previous cycles with good-quality embryos have failed to result in pregnancy, aneuploidy may be a factor.

Male factor infertility: Some evidence suggests that severe male factor may be associated with higher aneuploidy rates.

What PGT-A Can Do

• Identify embryos with correct chromosome number (euploid)
• Potentially reduce time to pregnancy by avoiding transfer of abnormal embryos
• Reduce miscarriage risk by selecting normal embryos
• Provide information about embryo sex (though this is not typically the reason for testing)

What PGT-A Cannot Do

• Test for all genetic conditions (only chromosome number, not specific genes)
• Guarantee a healthy baby (many conditions are not chromosomal)
• Guarantee pregnancy (euploid embryos still may not implant)
• Create normal embryos from abnormal ones (it selects, it does not fix)

The Controversy Around PGT-A

PGT-A is not universally recommended. Some controversy exists:

Mosaicism: Some embryos have a mix of normal and abnormal cells. These "mosaic" embryos are sometimes discarded but might have resulted in healthy pregnancies. The significance of mosaicism is still being understood.

Self-correction: There is evidence that some embryos with abnormal cells can self-correct during development.

Biopsy impact: Removing cells from an embryo carries a small risk of damage.

Cost-benefit: For younger women with good embryo numbers, the cost may not improve overall outcomes significantly.

Conflicting evidence: Some large studies question whether PGT-A improves live birth rates for all populations, though benefits are clearer for older women and those with recurrent loss.

PGT-M: Testing for Single Gene Disorders

PGT-M is used when one or both parents carry a known genetic mutation that causes a specific inherited condition.

What It Tests For

Single gene disorders are caused by mutations in individual genes. Examples include:

• Cystic fibrosis
• Sickle cell disease
• Thalassemia
• Tay-Sachs disease
• Huntington's disease
• BRCA1/BRCA2 mutations (breast/ovarian cancer predisposition)
• Fragile X syndrome
• Spinal muscular atrophy

The list of conditions that can be tested is extensive and growing.

Who Needs PGT-M?

Known carriers: If you or your partner are known carriers of a recessive condition, there is a 25% chance each embryo will be affected (if both carry it).

Dominant conditions: If one partner has a dominant condition like Huntington's disease, there is a 50% chance of passing it on.

Family history: If there is a family history of a genetic condition, carrier testing followed by PGT-M may be appropriate.

The Process

PGT-M requires more preparation than PGT-A:

1. Genetic counselling: Understanding your specific risks and what testing can offer.
2. Probe development: The lab creates a customised test specific to your mutation. This takes 4-8 weeks and has an upfront cost.
3. IVF cycle: Embryos are created and biopsied.
4. Testing: The custom probe identifies which embryos are affected, carriers, or unaffected.
5. Transfer: Only unaffected embryos (or unaffected carriers, depending on the condition) are transferred.

What PGT-M Can Do

• Prevent transmission of serious genetic conditions to children
• Provide peace of mind for carrier couples
• Avoid the difficult decision of whether to continue an affected pregnancy

Limitations

• Requires knowing the specific mutation in advance
• Custom test development takes time and money
• Not all conditions can be tested
• Does not test for other genetic issues (though PGT-A can be combined)

PGT-SR: Testing for Structural Rearrangements

PGT-SR is used when one partner carries a chromosomal translocation or other structural rearrangement.

What It Tests For

Translocations: Pieces of chromosomes have swapped places. The carrier is typically healthy (balanced translocation), but their embryos may inherit unbalanced arrangements, causing miscarriage or genetic conditions.

Other rearrangements: Inversions, deletions, duplications, and other structural abnormalities.

Who Needs PGT-SR?

• Individuals diagnosed with a balanced translocation
• Couples who have experienced multiple miscarriages and found a translocation during genetic workup
• Those with a family history suggesting a translocation

What PGT-SR Can Do

• Identify embryos with balanced or normal chromosomes
• Significantly improve success rates for translocation carriers (who otherwise have high miscarriage rates)

The Biopsy Process

For all types of PGT, cells must be removed from the embryo for testing.

When Biopsy Occurs

Day 5-6 biopsy (blastocyst stage): The most common approach. At this stage, the embryo has two distinct cell types: the inner cell mass (which becomes the baby) and the trophectoderm (which becomes the placenta). Cells are removed from the trophectoderm, leaving the inner cell mass undisturbed.

Day 3 biopsy (cleavage stage): Less common now. Removing cells at this earlier stage, when the embryo has only 6-8 cells, is more impactful and has largely been replaced by day 5 biopsy.

The Procedure

1. A small hole is made in the embryo's outer shell (zona pellucida) using a laser.
2. 5-10 cells are gently suctioned from the trophectoderm.
3. The cells are sent to a genetics laboratory for analysis.
4. The embryo is vitrified (frozen) while awaiting results.

Safety of Biopsy

Research suggests that properly performed biopsy does not significantly harm embryo development. However, it is an invasive procedure, and a small risk exists. The skill of the embryologist matters.

Results and What They Mean

PGT-A Results

Euploid: Normal chromosome number. Suitable for transfer.

Aneuploid: Abnormal chromosome number. Not recommended for transfer.

Mosaic: Mix of normal and abnormal cells. Decisions here are complex. Some mosaic embryos can result in healthy pregnancies, but risk depends on the type and extent of mosaicism.

No result: Sometimes testing fails, and the embryo status is unknown.

PGT-M Results

Unaffected: Does not carry the condition.

Carrier: Carries one copy of the gene (for recessive conditions, carriers are healthy but could pass the gene on).

Affected: Has the condition.

Decisions about transferring carrier embryos depend on the specific condition and family preferences.

Timing

Results typically take 1-2 weeks. During this time, embryos remain frozen.

Costs and Practical Considerations

Costs in the UAE

PGT adds significant cost to an IVF cycle:

Impact on Cycle Planning

Because results take time, PGT cycles are almost always freeze-all cycles. Fresh transfer is not possible. This means:

• Additional cost of frozen embryo transfer
• Additional time before knowing if pregnancy occurred
• No wasted transfers of abnormal embryos

Embryo Attrition

Not all embryos make it to testing. You might start with 10 eggs and end up with:

• 8 mature eggs
• 6 fertilised embryos
• 3 blastocysts suitable for biopsy
• 2 euploid embryos after testing

This "attrition funnel" is normal but can be emotionally challenging, especially if you end with no euploid embryos.

Making the Decision

Questions to Consider

What is my age? PGT-A benefits are clearest for women 38+. For younger women with many embryos, the value is less certain.

What is my history? Recurrent loss or failed transfers may make PGT-A more valuable.

Do we carry known genetic conditions? PGT-M is clearly indicated if so.

How many embryos do we expect? If you are likely to have only 1-2 embryos, testing may not be practical.

Can we afford it? PGT adds significant cost.

How would we feel about the results? Are we prepared for the possibility that no embryos pass testing?

Questions to Ask Your Doctor

"Do you recommend PGT for my specific situation?"

"What percentage of embryos at my age are typically euploid?"

"How do you handle mosaic results?"

"What are your lab's PGT success rates?"

Key Takeaways

• PGT-A tests chromosome number and is most beneficial for older women, recurrent loss, or repeated IVF failure.

• PGT-M tests for specific inherited conditions and requires advance preparation with custom probe development.

• PGT-SR is for chromosomal rearrangements like translocations.

• Testing requires embryo biopsy, which is generally safe but adds complexity.

• Not all embryos pass testing, and some results (like mosaicism) require nuanced decision-making.

• PGT adds cost and time but can improve efficiency by avoiding transfers of abnormal embryos.

• The decision should be individualised based on your age, history, finances, and values.

This content is for educational purposes only and should not replace professional medical advice or genetic counselling. Decisions about genetic testing involve complex considerations. Discuss your specific situation with your fertility team and a genetic counsellor.

Last updated: January 2026