PGT-M and PGT-SR: Preparing for IVF with Genetic Testing
Updated: 2 days ago
How preimplantation genetic testing can help families at risk of an inherited condition or chromosome rearrangement?
For people who know that a genetic condition or chromosome rearrangement may affect their family, planning a pregnancy can bring difficult questions. What is the chance of passing the condition on? Is embryo testing possible? How long will treatment take, and what is the realistic chance of having an embryo suitable for transfer?
Preimplantation genetic testing for monogenic conditions (PGT-M) and for structural chromosome rearrangements (PGT-SR) can help some patients reduce the risk of passing on a known genetic condition or reduce the risk associated with an unbalanced chromosome rearrangement. Both treatments require IVF, careful preparation and close coordination between the fertility, embryology and genetics teams.
At Consilium Clinic, we believe that good PGT care starts before ovarian stimulation begins. A clear diagnosis, an individual fertility assessment and realistic counselling can reduce avoidable delays and help patients understand each stage of the pathway.
What is PGT-M?
PGT-M is used when there is a known monogenic, or single-gene, condition in a family. It may be considered when one or both intended parents carry a specific genetic variant that could be passed to a child.
Examples include cystic fibrosis, sickle cell disease, Huntington's disease and some inherited cancer-predisposition conditions. The suitability of PGT-M depends on the particular condition, the identified genetic variant, its inheritance pattern and the relevant UK regulatory requirements.
The test is designed specifically around the family's genetic information. For this reason, the genetics laboratory usually needs to review the original genetic reports and may request DNA samples or information from relatives before treatment can begin.
What is PGT-SR?
PGT-SR is used when one intended parent carries a structural chromosome rearrangement, such as a balanced translocation or inversion.
A person carrying a balanced rearrangement is often healthy because the correct amount of genetic material is present, although it is arranged differently. During the formation of eggs or sperm, however, embryos may inherit an unbalanced arrangement with missing or additional chromosome material. This can result in failure of implantation, miscarriage or an affected pregnancy.
PGT-SR examines embryos for chromosome imbalances related to the known rearrangement, helping the team identify embryos considered suitable for transfer.
How are PGT-M and PGT-SR different from PGT-A?
The terms can be confusing, but they describe different tests.
PGT-M looks for a specific single-gene condition known to affect a family. PGT-SR looks for chromosome imbalances associated with a known structural rearrangement. PGT-A screens embryos for gains or losses involving whole chromosomes and is considered a fertility treatment add-on in the UK. For further information on PGT-A, please visit www.hfea.gov.uk/treatments/treatment-add-ons/pre-implantation-genetic-testing-for-aneuploidy-pgt-a/
PGT-A is therefore not interchangeable with PGT-M or PGT-SR. Whether any additional testing is appropriate should be discussed individually, including its limitations, possible effect on the number of embryos available for transfer and the current evidence.
Who may consider PGT-M or PGT-SR?
PGT may be discussed if:
you or your partner carry a known pathogenic genetic variant;
you have a child or previous pregnancy affected by a serious inherited condition;
there is a significant genetic condition in your family;
you or your partner carry a balanced chromosome rearrangement;
you have experienced recurrent miscarriage linked to a chromosome rearrangement; or
a clinical genetics team has advised that PGT may be an appropriate reproductive option.
PGT is a personal choice. Other reproductive options may include natural conception with prenatal diagnosis, the use of donor eggs or sperm, or adoption. Genetic counselling gives patients the opportunity to understand these choices and consider what feels right for them.
Why is IVF required?
PGT-M and PGT-SR can only be carried out on embryos created through IVF, even when a couple has no fertility problem.
The ovaries are stimulated to develop several follicles, eggs are collected, and mature eggs are fertilised, usually using intracytoplasmic sperm injection (ICSI). The embryos are cultured to the blastocyst stage. A small number of cells are then removed from the trophectoderm, the part expected to form the placenta and sent for genetic analysis.
The biopsied embryos are usually vitrified and stored while the results are awaited. If testing identifies an embryo suitable for transfer, a frozen embryo transfer can then be planned.
The PGT pathway at a glance
1. Review of the genetic diagnosis
We review the relevant molecular genetic report, chromosome result or family history. The specialist genetics laboratory must confirm that it can offer the appropriate test. For PGT-M, development and validation of a family-specific test may be required before IVF starts.
2. Genetic counselling
Counselling explains the inheritance pattern, the chance that an embryo may be affected or unbalanced, the limitations of testing and the alternatives to PGT. It also helps clarify which embryo results the patient would consider suitable for transfer.
3. Fertility assessment
The assessment commonly includes ovarian reserve testing, ultrasound evaluation of the ovaries and uterus, semen analysis and review of general health, medication and previous fertility or pregnancy history.
We also consider whether egg collection is likely to be technically straightforward and whether the uterine cavity and embryo-transfer route need further assessment.
4. Planning the laboratory pathway
The clinical, embryology and genetics teams confirm the testing strategy, consent requirements, sample arrangements and expected timescale. Completing these steps before stimulation can reduce delays later in treatment.
5. Ovarian stimulation and egg collection
Medication stimulates the ovaries to develop several eggs. The response is monitored with ultrasound scans and, where required, blood tests. Eggs are then collected under sedation or anaesthesia.
6. Fertilisation, embryo culture and biopsy
Mature eggs are fertilised and the resulting embryos are observed as they develop. Embryos that reach a suitable blastocyst stage may undergo biopsy before being vitrified.
7. Genetic results
The report may classify an embryo as suitable or unsuitable for transfer, depending on the condition and testing method. Occasionally, a sample produces no conclusive result. The implications of carrier balanced or inconclusive results should be discussed before treatment whenever possible.
8. Frozen embryo transfer
f a suitable embryo is available, the endometrium is prepared for transfer. Any anticipated technical difficulty with embryo transfer should be identified and addressed in advance. This may include a mock embryo transfer and, where clinically indicated, cervical dilatation before the actual transfer day.
What determines the chance of success?
Age is important because it influences egg number and egg quality, but it should not be considered in isolation. An individual assessment also considers:
ovarian reserve and response to stimulation;
the number of mature eggs obtained;
fertilisation and blastocyst development;
the inheritance pattern or type of chromosome rearrangement;
the proportion of embryos expected to be genetically suitable;
embryo quality and laboratory performance;
the uterine cavity and general reproductive health; and
whether at least one high-quality, genetically suitable embryo is available for transfer.
This is why two patients of the same age may have very different treatment prospects. Equally, a good ovarian response cannot guarantee a suitable embryo because embryos are lost naturally at each stage of development and some may carry the condition or chromosome imbalance being tested.
The most helpful counselling therefore follows the complete pathway: eggs collected, mature eggs, normally fertilised eggs, blastocysts available for biopsy, embryos producing a result and, finally, embryos suitable for transfer.
Could more than one IVF cycle be needed?
Yes. Some patients may not obtain a suitable embryo from their first cycle. This may be because few eggs are collected, embryos do not reach the blastocyst stage, a sample gives no result, or all tested embryos are affected or unbalanced.
Depending on ovarian reserve, age, previous response and personal circumstances, embryo or oocyte accumulation over more than one stimulation cycle may be discussed. The potential benefits, treatment burden, cost, and likelihood of obtaining a suitable embryo should be considered carefully.
Does PGT guarantee a healthy baby?
No. PGT reduces the risk associated with the condition being tested, but it cannot guarantee implantation, pregnancy, a live birth or a child unaffected by every possible health condition.
No genetic test is 100% accurate, and an embryo biopsy examines only a small sample of cells. Prenatal testing during pregnancy may therefore still be recommended after PGT. The genetics and maternity teams can discuss options such as chorionic villus sampling or amniocentesis, where appropriate.
Is embryo biopsy safe?
PGT-M and PGT-SR are considered established specialist treatments, and the HFEA states that there is no evidence that babies born after these treatments experience more health or developmental problems than babies born following IVF alone. However, IVF itself has risks, and there is a small possibility that an embryo may be damaged during biopsy. Some embryos may also produce an inconclusive result.
These limitations form an important part of consent and counselling.
How Consilium Clinic supports patients considering PGT
PGT treatment brings together reproductive medicine, genetics and embryology. Our role is to keep these parts of the pathway connected and understandable.
At Consilium Clinic, patients receive consultant-led assessment and an individual treatment plan. We review reproductive health alongside the genetic indication, coordinate with specialist genetics and embryology laboratories, assess the uterus and anticipated embryo-transfer route, and provide realistic counselling about possible attrition and the chance that more than one cycle may be required.
Our aim is to ensure that patients enter treatment informed, clinically prepared and supported throughout each stage.
Frequently asked questions
Can I have PGT if I am not infertile?
Yes. Many people considering PGT conceive naturally but require IVF so that embryos can be created, biopsied, and tested before transfer.
Can every inherited condition be tested?
No. The specific genetic cause must usually be known, the laboratory must be able to develop a reliable test, and UK regulatory requirements must be met. More than 2,000 conditions are currently approved for PGT-M in the UK. If a condition has not previously been approved, an application to the HFEA may be required.
Will every embryo reach the testing stage?
No. Not every egg will be mature, not every mature egg will fertilise and not every fertilised egg will develop into a blastocyst suitable for biopsy.
Will every tested embryo have a result?
Most biopsied embryos produce a result, but occasionally the sample is inconclusive or produces no result. The team will explain whether re-biopsy is possible and the potential implications.
If an embryo is suitable, will transfer result in pregnancy?
Not necessarily. A genetically suitable embryo still needs to survive warming, implant and develop normally. Embryo quality, the uterine environment and other reproductive factors remain relevant.
Should prenatal testing still be considered?
Yes. Because PGT is not completely diagnostic, prenatal testing may still be advised. This should be discussed with the genetics and maternity teams.
Taking the next step
If you have a known genetic condition, a chromosome rearrangement, a previous affected pregnancy or a family history that concerns you, an early specialist consultation can help clarify your options.
At Consilium Clinic, we can review your genetic information and reproductive history, arrange the appropriate fertility assessment and coordinate the next steps with the relevant genetics and laboratory teams.
Contact Consilium Clinic to arrange a consultation and receive an individual assessment of whether PGT-M or PGT-SR may be suitable for you.
Further information
Disclaimer:
Please note this information is intended for general education and does not replace individual medical or genetic advice. Treatment suitability, testing strategy and prognosis vary between patients.
