Preimplantation Genetic Diagnosis, Preimplantation Genetic Screening, and the Transfer of In Vitro Fertilized Embryos
© 2013 Elsevier Inc. All rights reserved. Preimplantation genetic diagnosis (PGD) is an alternative to methods of prenatal diagnosis, such as amniocentesis and chorionic villus sampling, allowing diagnosis of serious inherited disorders, but with the added advantage of avoiding the need to consider termination of an affected pregnancy. This benefit is achieved by performing the diagnosis on oocytes or early embryos before the time of pregnancy formation. An essential component of PGD is in vitro fertilization (IVF), as it is only with this procedure that oocytes and preimplantation embryos become accessible for analysis. In order to perform genetic diagnosis, polar bodies are removed from oocytes or cells are biopsied from embryos. The cells sampled can then be subjected to a variety of genetic tests for the diagnosis of single-gene mutations or chromosomal imbalance. Only embryos found to be free of the inherited mutation or chromosomal anomaly tested are transferred to the uterus and consequently any resulting pregnancy should be unaffected. As the efficiency of IVF treatments has improved, so pregnancy rates after PGD have increased, leading to a growing appreciation of this approach as an important reproductive option for patients at high risk of transmitting an inherited condition. Since the first PGD case, 20 years ago, more than 200 different inherited conditions have been diagnosed in human embryos, resulting in the births of thousands of healthy children.