PGT-M: testing embryos for an inherited condition

Who it is generally used for

PGT-M is for people who already know that a serious genetic condition runs in their family and want to reduce the chance of passing it on. A doctor may discuss it when, for example:

• both partners carry the same recessive condition, such as cystic fibrosis, so that each pregnancy has a one-in-four chance of being affected
• one partner has a dominant condition that can be passed on to children
• the woman carries an X-linked condition, such as haemophilia
• a previous child is affected, or a previous pregnancy was ended because of a serious genetic condition
• carrier screening or other genetic testing has already identified the gene change; see genetic history and testing

Recessive conditions are more common when partners are related by blood. For these couples, genetic testing comes first: PGT-M generally becomes possible only once the specific gene change in the family has been identified.

How a PGT-M cycle runs

Genetic counselling and the family work-up come first. A clinical geneticist or genetic counsellor confirms the diagnosis, reviews the family tree, and explains the options, the expected time-frame and the limits of testing. This step decides whether PGT-M is possible.

A test is prepared for the family. The laboratory designs and checks a test for the specific gene change, usually using DNA from both partners and from relatives whose status is known. This preparation is usually completed before ovarian stimulation starts.

Then an IVF cycle. Stimulation, egg collection and usually ICSI, which avoids extra sperm contaminating the test, are followed by culture to the blastocyst stage and the removal of a few cells from each embryo. The embryos are usually frozen while the laboratory reports, and an embryo found to be unaffected is transferred later; see IVF and ICSI.