PGD, or Preimplantation Genetic Diagnosis, is a relatively new technology. There are primarily two types of PGD that are performed. One type is to determine whether or not the chromosomal structure is normal, whether or not we have the proper numbers of chromosomes in an embryo. Another purpose of PGD can be to identify potentially single gene defects. These are diseases such as cystic fibrosis or muscular dystrophy. As a whole, PGD allows us to evaluate whether or not an embryo has a high or a low potential to be genetically abnormal. PGD is done as a part of the IVF process. Typically on the third day of laboratory culture of the embryo, a biopsy of the embryo is performed, where one of six or eight cells is removed. The cell is then analyzed to determine whether or not it has the proper chromosomal structure or the proper genetics, and that can help guide us in terms of the decision, two days later, as to which embryo we should be transferring back into the uterus.