Preimplantation genetic diagnosis (PGD) is a procedure whereby a single cell is removed from the embryo on day 3 to perform genetic testing. PGD can detect certain chromosomal abnormalities (i.e. trisomies, monosomies, translocations, etc.) and single gene defects (i.e. thalassemia, fragile X syndrome, etc.) and can also be performed for HLA typing.