What PGT stands for
PGT stands for preimplantation genetic testing — "preimplantation" because it happens before the embryo is placed in the uterus, "genetic testing" because it examines the embryo's chromosomes or genes. You may also see the older term PGD (preimplantation genetic diagnosis).
PGT is done on a blastocyst (a day 5–6 embryo) before transfer. An embryologist removes a few cells from the outer layer (the trophectoderm, not the part that becomes the baby). These cells are sent for genetic testing, while the embryo itself is frozen and waits for the result.
PGT-A vs PGT-M vs PGT-SR
| Type | Checks for | Ordered when |
|---|---|---|
| PGT-A (aneuploidy) | The embryo has the correct number of chromosomes | The general screening question most patients ask about |
| PGT-M (monogenic) | One specific inherited condition | A couple already knows they carry that condition |
| PGT-SR (structural rearrangement) | Chromosome structure issues | A parent already carries a balanced chromosomal rearrangement |
PGT-A is the one most patients mean when they just say "PGT" — a general chromosome-count screen. PGT-M and PGT-SR are targeted tests, ordered only when a specific genetic risk in the family is already known.
What it changes, and what it doesn't
PGT helps choose which tested-normal embryo to transfer first. It doesn't create better embryos. A normal result doesn't make pregnancy or a healthy baby certain, because implantation depends on more than chromosomes. It's discussed most often for recurrent implantation failure or recurrent pregnancy loss, older maternal age, or a known genetic condition. It is not a routine add-on for every cycle. See PGT: who actually benefits for more, including what a mosaic or abnormal result means.