PGT-A, PGT-M, PGT-SR: What’s the Difference?

Preimplantation genetic testing (PGT) is a way of analysing embryos during IVF before they’re transferred into the uterus. It can provide important information about chromosome health or specific genetic conditions. But there’s more than one kind of PGT - and each is designed for a different purpose.

How PGT Works

After fertilisation, embryos are grown in the lab to the blastocyst stage (day 5–6). A few cells are carefully removed from the trophectoderm (the layer that becomes the placenta) and sent for genetic analysis. The embryos are then frozen while awaiting results.

PGT-A: Preimplantation Genetic Testing for Aneuploidy

What it looks for:

• Checks for extra or missing chromosomes (aneuploidy), which can cause failed implantation, miscarriage, or genetic disorders like Down’s syndrome.

Who it’s for:

• Often recommended for patients over 35

• Those with recurrent pregnancy loss

• Couples with multiple failed IVF cycles

Key point:
PGT-A can’t improve embryo quality, but it can help select embryos more likely to result in a healthy pregnancy.

PGT-M: Preimplantation Genetic Testing for Monogenic Disorders

What it looks for:

• Screens for specific single-gene disorders (monogenic), such as cystic fibrosis, sickle cell anaemia, or Tay-Sachs disease.

• Requires prior knowledge of a family’s genetic mutation.

Who it’s for:

• Couples known to carry or be at risk for a specific inherited condition.

Key point:
This is targeted testing - it looks for a particular gene mutation, not a broad chromosomal check.

PGT-SR: Preimplantation Genetic Testing for Structural Rearrangements

What it looks for:

• Detects chromosomal rearrangements such as translocations or inversions, which can lead to unbalanced chromosomes in embryos.

Who it’s for:

• Individuals with known structural chromosome changes

• Couples with a history of repeated miscarriages or failed cycles linked to these changes

Key point:
PGT-SR helps identify embryos with the correct chromosome structure, increasing the likelihood of a healthy pregnancy.

Is PGT for Everyone?

No. While PGT can be incredibly valuable in certain situations, it isn’t recommended for all IVF patients. Reasons include:

• Additional cost and lab work

• The small risk that an embryo may not survive the biopsy or thawing process

• The possibility of no embryos passing the testing stage

Your fertility specialist will consider your medical history, age, previous IVF outcomes, and any known genetic risks before recommending PGT.

Bottom Line

• PGT-A: Screens for the right number of chromosomes.

• PGT-M: Tests for a specific inherited gene disorder.

• PGT-SR: Checks for correct chromosome structure in known rearrangements.

Each serves a different purpose - and the right choice depends entirely on your personal and medical circumstances.