Preimplantation genetic screening (PGS) is a test that determines if an embryo has a normal number of chromosomes (euploid) or an abnormal number of chromosomes (aneuploid). Some experts believe that PGS is valuable if a patient has had repeat failure with IVF or recurrent miscarriages. This test allows us to select only chromosomally normal embryos for transfer; however, transferring a ‘normal’ embryo does not guarantee a pregnancy, nor does it guarantee a healthy baby should a pregnancy make it to term. The purpose of PGS is to exclude chromosomally abnormal embryos from the transfer process.
Preimplantation genetic diagnosis (PGD) is a test that determines if an embryo carries a specific gene that is associated with a particular disease. Examples include Huntington’s Disease, Cystic Fibrosis, and Tay Sachs. PGD is often used to eliminate embryos carrying the specified gene from the transfer process to ensure that any resulting live births are not affected by the disease.
Both PGS and PGD require an embryo biopsy to obtain a sample for testing. This is achieved by lasering a small hole in the outer layer of the embryo and removing a few cells from the embryo. These types of tests carry inherent risks which will be discussed with you at length should you consider PGS or PGD as part of your treatment.