Here is a concise overview of how preimplantation genetic diagnosis (PGD) is performed:

1. IVF Cycle: The process begins with an IVF cycle, where eggs are retrieved and fertilised with sperm to create embryos.

2. Embryo Development: The embryos are cultured and allowed to develop to the blastocyst stage for 5 or 6 days after fertilisation.

3. Embryo Biopsy: A small number of cells are removed from each embryo, usually from the trophectoderm layer, which will form the placenta. This can be done on day 3 (cleavage stage) or day 5/6 (blastocyst stage).

4. Genetic Testing: The biopsied cells are sent to a genetic testing lab to analyse specific genetic disorders or chromosomal abnormalities. Techniques such as PCR, FISH, CGH, or next-generation sequencing are used for this purpose.

5. Embryo Freezing: After the biopsy, the embryos are frozen using vitrification. This helps to preserve them until the genetic test results are available.

6. Results: The genetic testing results are typically available within 1-2 weeks after the biopsy. If the embryos are deemed suitable, they are thawed and transferred to the uterus.

7. Embryo Transfer: One or more genetically normal embryos are selected for transfer to the uterus. This selection is based on the PGD results and the embryo’s developmental potential.