PGT embryo testing
PGT tests IVF embryos before one is chosen for transfer. The most common form, PGT-A, checks for the right number of chromosomes; PGT-M and PGT-SR look for a specific condition or chromosome change that runs in the family.
With Datuk Dr. Navdeep Singh Pannu, FRCOG, at Alpha IVF & Women's Specialists, Kota Damansara
- Done during
- An IVF cycle, on embryos grown to day 5 or 6
- Sample
- A few cells from the outer layer of each embryo
- While you wait
- The embryos are frozen until the results are back
- Transfer
- A frozen embryo transfer in a later cycle
What it is
Many embryos that look healthy under the microscope carry too many or too few chromosomes. These embryos often fail to implant or end in miscarriage, and the chance of this rises with the woman's age.
In PGT-A (preimplantation genetic testing for aneuploidy), the embryologist takes a few cells from the outer layer of each embryo, the part that later forms the placenta, and the laboratory counts the chromosomes. Embryos with a normal count are then transferred one at a time.
Two related tests look for something more specific. PGT-M (for monogenic conditions) checks embryos for a single inherited condition that one or both partners carry, such as thalassaemia, which is common in Malaysia, or haemophilia. PGT-SR (for structural rearrangements) is for couples where one partner carries a chromosome change such as a balanced translocation, which can cause repeated miscarriage.
Both start with genetic tests on the parents to confirm the exact change. For PGT-M, the laboratory then builds a test for your family's gene before the IVF cycle begins, which can take several weeks. The embryos are biopsied and frozen in the same way as for PGT-A.
Who it can help
- Women aged 35 or over having IVF
- Two or more miscarriages
- Repeated embryo transfers that have not implanted
- A previous pregnancy with a chromosome condition
- Couples who want to transfer one embryo at a time with more confidence
- Couples who both carry the same inherited condition, such as thalassaemia, or who already have a child affected by one (PGT-M)
- A partner with a balanced translocation or other chromosome rearrangement (PGT-SR)
How it works
-
IVF to the blastocyst stage
You go through ovarian stimulation and egg collection as in a normal IVF cycle. The embryos are grown in the laboratory to day 5 or 6.
-
Embryo biopsy
The embryologist removes a few cells from the outer layer of each good-quality embryo. The cells that will become the baby are not touched.
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Freezing
Each embryo is frozen straight after its biopsy while the cells are sent for testing.
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Results
Dr. Navdeep goes through the report with you: which embryos have a normal chromosome count and which do not.
-
Frozen embryo transfer
In a later cycle your womb lining is prepared, and a single embryo with a normal result is thawed and transferred.
Good to know
Side effects and risks
- Some cycles produce no embryos with a normal result, so there is nothing to transfer
- A few embryos give a "mosaic" or unclear result, which needs a careful talk before any decision
- No test is perfect; routine pregnancy screening is still advised
- It adds laboratory costs to the IVF cycle
What it cannot do
PGT-A does not improve the quality of your embryos; it helps choose between the ones you have. A normal result raises the chance that a transfer works, but it is not a guarantee.
Is it right for you?
For younger women with plenty of embryos the benefit is smaller. Dr. Navdeep will talk through whether testing is worth it in your case before you start.
Planning PGT-M or PGT-SR
Bring any genetic reports you have, for both partners. Setting up the test adds time before the cycle, and genetic counselling helps you understand the results and what they mean for your family.
Other tests after failed transfers
When healthy embryos still do not implant, tests of the womb lining can help time the transfer. These are covered on the after a failed IVF page.
Questions people ask
Does the biopsy harm the embryo?
The cells are taken from the outer layer that forms the placenta, not from the part that becomes the baby. Embryos are handled by experienced embryologists, and a biopsied embryo can go on to a normal pregnancy.
How long do the results take?
Usually a few weeks. Because the embryos are frozen, there is no rush: the transfer is planned for a later cycle when your lining is ready.
Can PGT-A tell the sex of the embryo?
The test reads the sex chromosomes, but embryos are not chosen by sex for non-medical reasons.
We are both thalassaemia carriers. What are our options?
If you both carry the same type of thalassaemia, each pregnancy has a one in four chance of being affected. A DNA blood test for both of you confirms the types first. Options include testing in pregnancy, or IVF with PGT-M so that an unaffected embryo is transferred. Dr. Navdeep can talk you through both.
Should we test if we have only one or two embryos?
Sometimes it still helps, especially after repeated miscarriage. Sometimes it is better to transfer without testing. This is a decision to make together, based on your age and history.
Further reading
This page is general information and does not take your personal circumstances into account. Please speak to your doctor for advice that is right for you. Disclaimers