PGD is recommended to identify embryos that are at risk for a single gene disorder, e.g. cystic fibroses, and for testing for chromosomal structural rearrangements, e.g. translocations, deletions/duplications. PGS or now called PGT, preimplantation genetic testing, is used to detect aneuploidy.
Read the full article on: What is the Preimplantation Genetic Diagnosis (PGD)? ( 53).