Genetic carrier screening and PGT-M: who it is for and what it involves

Some people arrive at a fertility clinic already knowing a genetic condition runs in the family. Others find out during the workup, when a routine screening test turns up something nobody was looking for. Either way, the questions that follow are the same, and they are more answerable than they first appear.

Two different tests, often confused

Carrier screening looks at you. It checks whether you carry a gene variant for a recessive condition — something you can pass on without ever having any sign of it yourself. Many recessive conditions require a copy from each parent, which is why carrier screening usually looks at both partners: one carrier is common and generally unremarkable, two carriers of the same condition is the finding that changes a plan.

PGT-M looks at embryos. If a specific inheritable condition is known to be in play, embryos created through IVF can be tested for it before transfer.

The order matters. Carrier screening tells you whether there is anything to test for. PGT-M is what you do about it.

What PGT-M actually is

The HFEA describes PGT-M — previously called PGD — as a test used alongside IVF to examine embryos before transfer, and notes it can be used to test for more than 2,000 rare genetic conditions, cystic fibrosis and early-onset Alzheimer’s among them.

It is for people who know a serious inheritable condition is in the family and want to avoid passing it on. It is not a general health screen of an embryo, and it does not answer questions other than the one it was set up to answer: each test is built around a specific, known condition.

One practical detail worth knowing early: approval can be required. The HFEA notes that some conditions are already pre-approved while rarer ones may need a clinic to get approval first. Regulatory arrangements differ by country, but the general shape — that testing for a specific rare condition is a process with lead time, not a box you tick — tends to hold. Ask about it at the start rather than mid-cycle.

How it changes a treatment plan

It usually means IVF, even if you would not otherwise need it. Testing embryos requires embryos in a laboratory. For couples who conceive easily but carry a condition, this is the part that takes adjusting to.

It almost always means freezing. Test results take time, so embryos are frozen while you wait and transferred in a later cycle. If you are travelling for treatment, that makes a two-trip structure close to certain — the arrangement described in freeze-all and the two-trip treatment.

It adds a stage to the funnel. Not every embryo will be suitable for testing, and not every tested embryo will be suitable for transfer. Ask your clinic to walk you through the realistic numbers for your situation before you start, so the updates are not a series of surprises.

It adds cost and time. Both belong in the plan from the beginning, which is the reasoning behind asking what a quote does not cover.

Questions worth asking

• Should we both have carrier screening, and which panel?
• If we are both carriers, what are the options? PGT-M is one. Donor gametes are another. Prenatal testing in a natural pregnancy is another. Which are available and appropriate depends on the condition and on where you are treating.
• Is this condition already approved for testing, or does approval need to be sought? How long does that take?
• How many embryos would you expect to be testable, realistically?
• What happens to embryos that carry the condition? Worth deciding before the question arrives, alongside the broader storage questions in the embryos you do not use.

On genetic counselling

If a condition is confirmed in your family, ask to speak to a genetic counsellor rather than working it out from the internet or from a fertility consultation alone. Inheritance patterns are specific, the probabilities are frequently misunderstood, and the implications reach beyond this pregnancy to siblings and other relatives.

It is a conversation most people find steadying rather than alarming, because vague dread is replaced by a defined picture and a set of actual options.

If you are treating abroad

Two additions. Ask what the clinic can test for and what has to be arranged in advance, because setting up a test for a specific rare condition is not instant. And bring the documentation: if a relative has a confirmed diagnosis, the genetic report naming the exact variant is the single most useful document you can arrive with. Without it, a clinic may be starting from scratch.

This article is general information, not medical advice. What applies to your family is a question for a clinician and a genetic counsellor with your history in front of them.

For how testing fits into the wider process, read the patient journey.