Preimplantation genetic testing (PGT) checks embryos created through IVF or ICSI before one is transferred. A few cells are taken from the outer layer of a day 5 embryo and analysed. PGT can help in specific situations, but it is not 100% accurate and does not replace pregnancy testing.
What PGT is
PGT is genetic testing of embryos before transfer. It always requires IVF or ICSI, even for people without a fertility problem, because the embryos must be grown in the lab.
| Type | What it looks for | Typical reason |
|---|---|---|
| PGT-M | A known single-gene condition in the family | Both or one partner carry a serious inherited condition |
| PGT-SR | Structural chromosome changes such as translocations | A parent carries a chromosome rearrangement |
| PGT-A | Missing or extra chromosomes (aneuploidy) | Sometimes offered after recurrent miscarriage or at older age |
PGT-M is approved in the UK for over 2,000 genetic conditions. PGT-A does not look for specific diagnoses; it checks whether an embryo has the usual number of chromosomes.
Who it is for
- Couples with a family history of a serious genetic condition
- People who have ended a previous pregnancy because of a genetic condition
- A partner who carries a chromosome rearrangement
- Recurrent miscarriage, where PGT-A may reduce miscarriage risk
The UK regulator rates PGT-A as not effective for improving the chance of a baby for most patients, though it may reduce miscarriage. Ask your doctor whether it fits your situation.
Step by step
- Counselling firstYour doctor reviews your family history and any genetic reports to decide which type of PGT fits your situation.
- IVF or ICSIEggs are collected and fertilised, often using ICSI when embryos will be tested.
- Culture to blastocystMost testing takes place at the blastocyst stage, around day 5 to 7.
- Trophectoderm biopsyA few cells are removed from the trophectoderm, the outer layer that forms the placenta. The inner cell mass, which forms the baby, is not touched.
- Freezing while testingEmbryos are now usually frozen while the cells are analysed, and transferred in a later cycle.
- Results and transferYour doctor explains the results, and one unaffected embryo may be chosen for transfer.
What it feels like and what results mean
The biopsy happens in the lab, so you feel nothing extra. Your experience is an IVF cycle followed, usually, by a frozen embryo transfer. The added time can make the path to pregnancy longer.
- Unaffected or euploid: no abnormality found in the cells tested, which is not a guarantee of a healthy pregnancy.
- Affected or aneuploid: an abnormality was found; such embryos have less chance of developing into a baby.
- Mosaic: a mix of normal and abnormal cells; chances may be lower, but healthy births after mosaic transfer have been reported.
- No result: sometimes the test does not work and gives no answer.
How to prepare
- Bring any family genetic reports to your first visit
- Ask what each possible result would mean for your embryos
- Plan for prenatal testing if you become pregnant
- Do not assume PGT finds every genetic problem
- Do not assume PGT-A will raise your chance of a baby
- Which type of PGT is being offered, and why for us?
- What happens if an embryo shows a mosaic or unclear result?
- What is the total cost, including freezing and storage?
- Will we see a genetic counsellor before and after testing?
Risks and limits
| Limit | What sources say |
|---|---|
| Embryo damage | Removing cells may damage an embryo and stop it developing. |
| Wrong result | Not 100% accurate; it may miss an abnormality or report one that is not there. |
| Mosaicism | The biopsy may not represent the whole embryo; one study cites 70% to 93% agreement between biopsy and whole blastocyst. |
| Discarded embryos | A false abnormal result could lead to a viable embryo not being used. |
| Children's health | No evidence that babies after PGT-M or PGT-SR have more health problems than after IVF alone. |
Because PGT can give false results, prenatal screening or diagnostic testing is still advised in pregnancy. After PGT-M, studies advise CVS or amniocentesis.
- PGT-A counts chromosomes; it does not give specific genetic diagnoses.
- Misdiagnosis is possible, for example because of mosaicism (a mix of normal and abnormal cells).
- The biopsy can sometimes damage an embryo and stop it developing.
- It adds cost, and it is not funded by the NHS in the UK.
HFEA says there is little evidence that PGT-A improves the chance of having a baby for most fertility patients, and there is no guarantee it will. Discuss whether it fits your situation.
PGT-M (for single-gene conditions) and PGT-SR (for structural chromosome rearrangements) have a clearer purpose: they are used when a known inherited condition runs in the family. Your clinic should offer genetic counselling before testing.
How DBN does it
- PGT uses a biopsy of a few trophectoderm cells (the layer that forms the placenta), not the inner cell mass.
- Embryos are cultured to day 5 (blastocyst) and can be vitrified and stored at −196 °C.
- PGT is an add-on of about 35,000–55,000 THB. First consultation is free; prices are confirmed at consultation.
When to see a doctor
- A serious genetic condition runs in your family
- Carrier screening showed you and your partner carry the same condition
- You or your partner carry a chromosome rearrangement
- You have had repeated miscarriages
Questions & answers
Does the biopsy harm the baby-forming cells?
Cells are taken from the trophectoderm, not the inner cell mass. Even so, removing cells can sometimes damage an embryo.
If my embryo is normal, do I still need prenatal tests?
Yes. PGT is not 100% accurate, so prenatal screening or diagnostic testing is still advised.
Can a mosaic embryo be transferred?
Sometimes. Chances may be lower, but healthy births have been reported. Discuss this carefully with your doctor.
Related DBN services
Related articles
Sources
- Pre-implantation genetic testing for aneuploidy (PGT-A) — HFEA
- Frequently asked questions about PGT-A — HFEA
- PGT-M and PGT-SR — HFEA
- Preimplantation genetic testing — NHS England Genomics Education Programme
- Should non-invasive prenatal testing be recommended for patients who achieve pregnancy with PGT? (BMC Pregnancy and Childbirth, 2024) — PubMed Central