Preimplantation genetic testing is genetic testing performed on embryos that have been created through in vitro fertilization prior to being transferred into the woman’s uterus. It is typically done to identify chromosome number issues or specific genetic defects in the embryo.
When the embryo is screened to determine the number of chromosomes, the process is called preimplantation genetic screening or aneuploidy screening. In cases where one or both parents are known to have a genetic abnormality and testing is carried out to determine whether or not the embryo also carries that abnormality, it is referred to as preimplantation genetic diagnosis.
During in vitro fertilization, the eggs are retrieved then inseminated with sperm to create embryos. The development of these embryos is closely monitored, and by day 5-6 after egg retrieval they should be at what is called the blastocyst stage. At this point, a few cells can be removed, or biopsied, from each embryo and undergo genetic testing.
In the case of PGS, testing is performed to determine the number of chromosomes contained in each embryo. In the case of PGD, a different type of test is performed to determine if each embryo carries the specific disease of interest.
Many reproductive endocrinologists offer preimplantation genetic testing to couples undergoing in vitro fertilization prior to embryo transfer. For couples at risk of having a child affected with a known genetic disease (like cystic fibrosis), PGD enables them to avoid passing this disease on to future generations. For couples pursuing PGS, identifying which embryos are chromosomally normal can increase the chance of pregnancy while reducing the risk of miscarriage and multiple pregnancy (twins, triplets, etc).
Those who might benefit from preimplantation genetic testing include the following:
