What is PGT-A?

PGT-A — preimplantation genetic testing for aneuploidy — checks embryos created through IVF for the correct number of chromosomes before transfer. A normal embryo has 46 chromosomes. Errors in cell division can leave an embryo with too many or too few, and most such embryos either fail to implant or miscarry. How it works: around day 5 or 6, a few cells are removed from the outer layer of the embryo — the part that becomes the placenta, not the baby. Those cells are analysed and the embryo is frozen while results come back. That detail about which cells are sampled explains most of PGT-A's limitations. The biopsy tests placental-lineage cells, and they usually reflect the embryo but not always. What PGT-A does not do: It does not test for inherited conditions like thalassaemia or cystic fibrosis — that is PGT-M. It does not detect structural abnormalities. It does not create good embryos. It selects among the embryos you already have. That last point is the one most worth holding onto. PGT-A cannot improve embryo quality — it can only tell you more about what you have. If all your embryos are affected, PGT-A has not caused that; it has revealed it. Whether it improves your chance of a baby is a genuinely contested question, addressed separately below.