Testing Embryos for a Known Genetic Condition

What PGT-M and PGT-SR test for

Both are forms of preimplantation genetic testing done on embryos created through IVF, before any embryo is transferred. PGT-M — preimplantation genetic testing for monogenic disorders — is used when a couple is known to carry a specific single-gene condition, such as cystic fibrosis, sickle cell disease, Tay-Sachs, Huntington's disease, or a hereditary cancer variant like BRCA. It sorts embryos into affected, unaffected, and sometimes carrier.

PGT-SR — for structural rearrangements — is used when one partner carries a balanced chromosomal rearrangement, such as a translocation or inversion. The carrier is usually healthy, but their embryos can inherit an unbalanced amount of chromosome material, which often leads to failed implantation or miscarriage. Couples in this situation are frequently identified during the workup after recurrent pregnancy loss.

How PGT-M and PGT-SR differ from PGT-A

This is the distinction that matters most, because the three tests get lumped together. PGT-A screens every embryo for the wrong number of chromosomes — aneuploidy — as a general bet on which embryo is most likely to implant. Major professional guidance holds that PGT-A has not been shown to raise live-birth rates when used routinely across the general IVF population 1Ref 1Practice Committees of ASRM and SART (2024).The use of preimplantation genetic testing for aneuploidy: a committee opinion.That the value of PGT-A as a routine screen for all IVF patients has not been demonstrated — used to contrast broad aneuploidy screening with targeted testing for a known condition., and a large multicenter randomized trial found no improvement in ongoing-pregnancy rates versus choosing embryos by appearance in good-prognosis patients 2Ref 2Munné S, et al. (STAR Study Group) (2019).Preimplantation genetic testing for aneuploidy versus morphology as selection criteria for single frozen-thawed embryo transfer in good-prognosis patients: a multicenter randomized clinical trial.The STAR RCT found PGT-A did not improve ongoing-pregnancy rates versus morphology-based selection in good-prognosis patients — evidence that PGT-A is not shown to raise live-birth rates for the general IVF population..

PGT-M and PGT-SR are different in kind, not just degree. They do not screen for a general risk; they answer a specific, known question — does this embryo carry the family's condition, or an unbalanced version of the parent's rearrangement? That targeted purpose is why the ongoing debate about whether pgt-a actually improves ivf success does not settle the value of PGT-M or PGT-SR. The UK regulator publishes a five-tier, color-coded rating of IVF add-ons, and broad screens marketed to the general population are exactly what that scrutiny targets 3Ref 3Human Fertilisation and Embryology Authority (2024).Treatment add-ons with limited evidence.The UK regulator's five-tier, color-coded rating of IVF add-ons, in which broad screens marketed to the general population face scrutiny for limited evidence.; a diagnostic test for a known inherited condition sits in a different category. If you are still sorting out PGT-A testing from these targeted tests, the dividing line is a known condition versus a broad screen.

How the testing fits into an IVF cycle

The embryo side of the process looks like any IVF cycle until the lab step. Eggs are retrieved and fertilized, embryos grow to the blastocyst stage around day five or six, and a few cells are gently biopsied from the trophectoderm — the part that becomes the placenta, not the baby. Those cells go to a genetics lab while the embryo itself is frozen.

Two details are specific to PGT. Fertilization is usually done with ICSI, injecting a single sperm into each egg, because stray sperm clinging to the outside of an embryo could contaminate the genetic sample; major guidance lists PGT as one of the recognized reasons to use ICSI rather than applying it to everyone by default 4Ref 4Practice Committees of ASRM and SART (2026).Intracytoplasmic sperm injection for nonmale factor indications: a committee opinion.That ICSI is an add-on justified by specific indications including PGT, rather than a default upgrade for everyone — the basis for using ICSI to avoid sperm contamination of the genetic sample.. And because the lab needs time to run the test, PGT cycles are typically freeze-all: embryos are cryopreserved and transferred in a later cycle. That timing is not a disadvantage on its own — a large randomized trial in ovulatory women found live-birth rates after frozen and fresh transfer were essentially the same 5Ref 5Shi Y, et al. (2018).Transfer of Fresh versus Frozen Embryos in Ovulatory Women.An RCT in ovulatory women without PCOS found live-birth rates did not differ significantly between frozen and fresh transfer — so the freeze-all timing PGT requires is not a disadvantage in itself.. Embryo grading by appearance still happens alongside the genetic result, and the two pieces of information are read together.

Building a PGT-M test takes preparation

For PGT-M specifically, the lab usually builds a custom test tailored to your family's exact mutation before the IVF cycle begins. This setup step often uses DNA from both partners and sometimes from relatives or an affected family member, so the lab can reliably distinguish an affected embryo from an unaffected one. It typically needs to be arranged weeks ahead of the cycle rather than added at the last minute.

The preparation time is routine planning, not a warning sign. PGT-SR setups are often more standardized, since the target is a known chromosomal rearrangement rather than a single DNA letter. Asking early how long the setup will take — and what DNA samples are needed — keeps the genetic prep from delaying the IVF cycle itself, which is the practical reason these tests are planned well in advance.

What a PGT-M or PGT-SR result can and cannot tell you

A result identifies which embryos carry the specific condition being tested and which do not — that is its entire job, and within that job it is powerful. What it does not do is guarantee a baby, or a healthy one. It does not screen for conditions it was not designed to find, it cannot rule out every genetic or developmental problem, and no biopsy result is infallible, which is why many clinics still offer confirmatory testing during a resulting pregnancy.

After testing, the usual practice is to transfer a single unaffected embryo. Guidance supports elective single-embryo transfer because moving one tested blastocyst keeps pregnancy rates comparable while sharply lowering the risk of twins and the complications that come with them 6Ref 6Practice Committees of ASRM and SART (2021).Guidance on the limits to the number of embryos to transfer: a committee opinion.That transferring a single tested blastocyst keeps pregnancy rates comparable while sharply lowering multiple-gestation risk — the basis for single-embryo transfer after PGT.. One hard possibility deserves naming up front: a cycle can end with no unaffected embryos to transfer. Knowing that outcome is on the table — and what the next step would be — is part of going in with clear eyes.

Questions worth asking before you start

A few specific questions turn PGT-M or PGT-SR from a black box into a plan. Because the test is only as good as the lab running it, the accuracy and no-result rate of that particular lab matter more than the brand name on the brochure. Cost is worth pinning down early, since genetic testing sits outside most base IVF fees and is billed per embryo.

• What is this lab's reported accuracy and no-result rate for my specific condition?
• How long will the PGT-M setup take, and whose DNA is needed?
• What is the genetic testing lab cost per embryo, and is confirmatory prenatal testing recommended?
• What are the embryo storage fees while we wait, and afterward?
• What happens if no unaffected embryos are found in a cycle?

Because these are genetic decisions with real weight, working with a certified genetic counselor — not only the fertility clinic — helps you understand what a result means for your family before any transfer.