Overview
Preimplantation genetic testing for aneuploidy (PGT-A), previously called PGS, checks IVF embryos for missing or extra chromosomes. An embryologist removes a few cells from each embryo, usually at the blastocyst stage on day five or six, and the cells are tested. Embryos with the expected number of chromosomes are reported as euploid, those with missing or extra chromosomes as aneuploid, and some are reported as mosaic, meaning they appear to contain a mix of both.
PGT-A is different from testing for a known inherited condition (PGT-M for single-gene conditions, or PGT-SR for chromosome rearrangements). Those tests look for a specific problem a family is known to carry. PGT-A is a screening test offered to people with no known genetic condition, on the idea that choosing a chromosomally normal embryo will improve the chance of a baby.
The evidence for that idea is limited. The UK regulator, the HFEA, rates PGT-A red for increasing the chance of having a baby for most fertility patients: on balance, the evidence suggests it may reduce effectiveness, in part because it often leaves fewer embryos to transfer. The HFEA rates it green for reducing the chance of miscarriage for most patients, and grey (not enough evidence to rate) for both outcomes in older women. ESHRE's 2023 good practice recommendations say PGT-A is not recommended for routine clinical use, and a 2024 ASRM committee opinion says its value as a routine test for all IVF patients has not been demonstrated.
Who it's for
- People who have discussed the evidence with a specialist and want to know about their embryos' chromosomes, accepting that it may not improve their chance of a baby.
- People for whom a lower chance of miscarriage per transfer matters, bearing in mind that it does not remove the risk.
- It is often offered to older patients and to those with repeated miscarriage or repeated failed transfers, though the HFEA notes the evidence for these groups is less reliable.
- People with a known inherited condition need a different, targeted test (PGT-M or PGT-SR), usually after genetic counselling.
Whether a treatment suits you depends on your own history and tests — discuss it with a fertility specialist.
Step by step
Counselling and consent
Before starting, the clinic should explain what the test can and cannot show, what happens to embryos reported as aneuploid or mosaic, and the cost. Ask what the clinic does with mosaic embryos before you consent.
IVF or ICSI cycle
Stimulation and egg collection follow the usual IVF steps. ICSI is often used so that stray sperm cannot contaminate the sample.
Embryo culture to blastocyst
Embryos are cultured for five to six days. Only those that reach the blastocyst stage and are judged suitable can be biopsied.
Biopsy
A few cells are removed from the outer layer of each blastocyst, the part that would become the placenta. The embryos are then frozen while the cells are tested.
Laboratory testing
The cells are sent to a genetics laboratory, which commonly uses next-generation sequencing (NGS) to count the chromosomes. Results usually take one to a few weeks.
Results and genetic counselling
Each tested embryo is reported as euploid, aneuploid, mosaic or, sometimes, no result. A specialist or genetic counsellor should talk you through the report and the options for each embryo.
Frozen embryo transfer
A selected embryo is thawed and transferred in a later cycle. Remaining euploid embryos stay frozen for future use.
Typical timeline
- IVF stimulation and egg collection
- About 2–3 weeks, as for IVF
- Culture to blastocyst and biopsy
- 5–6 days after egg collection
- Testing and results
- Usually 1–3 weeks, depending on the laboratory
- Preparing for a frozen embryo transfer
- Usually 2–4 weeks, often in a later menstrual cycle
- Whole process
- Typically 2–3 months from stimulation to pregnancy test, often over two trips
What it costs
PGT-A adds substantially to the cost of IVF, and is usually priced by number of embryos tested. Bangkok Hospital publishes a PGT-A and embryo freezing package for two embryos at 96,000 baht (valid to 31 December 2026). MedPark's IVF/ICSI package with PGT-A for up to five embryos is 380,000 baht against 280,000 baht for its basic package (Thai nationals and residents only), and Superior A.R.T. publishes all-inclusive IVF/ICSI with PGT-A packages of 495,000 and 498,000 baht on different pages. Ask whether the price covers biopsy, freezing, storage and the frozen transfer, and what each extra embryo costs.
Risks and side effects
- Fewer embryos to transfer: the HFEA notes that PGT-A often reduces the number of embryos available, and for most patients the time to a live birth may be longer.
- Wrong results: the test can miss an abnormality or report one that is not there, so healthy embryos may be discarded.
- Mosaic results are hard to interpret. Mosaic embryos may have a lower chance of pregnancy, but healthy births have been reported after their transfer.
- The biopsy can damage an embryo and stop it developing.
- No embryo may be suitable for transfer if all tested embryos are reported as abnormal.
- The HFEA says PGT-A carries no additional known risks for the person having treatment beyond those of IVF itself.
Questions to ask a clinic
- Why are you suggesting PGT-A for me, and what evidence supports it for someone in my situation?
- Which laboratory does the testing, which method does it use, and how often does it report no result?
- What do you do with embryos reported as mosaic? Would you transfer one?
- What happens to embryos reported as aneuploid?
- How many blastocysts would you expect me to have available for biopsy?
- What does the testing cost per embryo, and what does a frozen transfer cost?
- Would you recommend transferring an untested embryo instead, and why or why not?
Frequently asked questions
Does PGT-A improve the chance of having a baby?
For most patients, current evidence says no. The HFEA rates it red for this purpose, and ESHRE does not recommend it for routine use. The HFEA rates it green for reducing miscarriage, which is not the same as increasing the chance of a baby.
What does the HFEA's red rating mean?
The HFEA uses a traffic-light system for treatment add-ons. Red means that, on balance, moderate or high quality evidence suggests the add-on may reduce treatment effectiveness, or that there are safety concerns. For PGT-A, it reflects the loss of embryos that might have led to a baby.
Is PGT-A the same as testing for a genetic disease?
No. PGT-M and PGT-SR look for a specific inherited condition or chromosome rearrangement known to run in a family. PGT-A screens for abnormal chromosome numbers in people with no known condition.
What is a mosaic embryo?
One whose tested cells appear to contain both normal and abnormal chromosome numbers. It may have a lower chance of pregnancy, but healthy births have been reported. Ask your clinic about its policy before testing.
Does PGT-A mean I will need a frozen embryo transfer?
Usually, yes. Because results take time, tested embryos are normally frozen and transferred in a later cycle.
Should I have PGT-A?
That depends on your age, history and how you weigh the possible benefits and drawbacks. Discuss it with a fertility specialist, and ask for the evidence behind any recommendation.
