Preimplantation genetic testing is a technique used to identify genetic defects in embryos created through in vitro fertilization (IVF) before pregnancy. Preimplantation genetic diagnosis (PGD) refers specifically to when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality.
Because only unaffected embryos are transferred to the uterus for implantation, preimplantation genetic testing provides an alternative to current postconception diagnostic procedures (ie, amniocentesis or chorionic villus sampling), which are frequently followed by the difficult decision of pregnancy termination if results are unfavorable. PGD is presently the only option available for avoiding a high risk of having a child affected with a genetic disease prior to implantation.
PGD is used to identify chromosomal disorders in which a variety of chromosomal rearrangements, including translocations, inversions, and deletions, can be detected using fluorescent in situ hybridization (FISH). Some parents may have never achieved a viable pregnancy without using PGD because previous conceptions resulted in chromosomally unbalanced embryos and were spontaneously miscarried.
In order to have embryos to biopsy for PGD, patients must undergo in vitro fertilization (IVF). After fertilization of the egg with sperm, embryos are allowed to develop into cleavage-stage embryos. On day 3 after egg retrieval (equivalent to 2 days after fertilization), a single blastomere is removed from the developing embryo for performance of FISH or PCR for genetic evaluation of the embryo. Nonaffected or normal embryos are then transferred into the uterus for subsequent implantation/pregnancy.
PGD Details
