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Preimplantation Genetic Testing (PGT)
Preimplantation genetic testing, also known as embryo biopsy, is used to identify chromosomal or genetic defects in embryos prior to an in vitro fertilization (IVF) cycle. Genetic defects are a primary cause of both the failure of an embryo to implant and subsequent miscarriage after successful implantation. There are two types of genetic tests available for embryo evaluation: Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS). PGD is used to diagnose a specific, single genetic defect that is known to be carried by one or both parents. This can be because the parent has that defect, such as muscular dystrophy, or because it is present in one of their families’ histories. If PGD identifies an embryo with that genetic defect that risks a child with that disease, the embryo is not selected for implantation in the uterus, and a non-affected embryo is used instead.
PGS is often confused with PGD. The difference between the two is that PGS evaluates embryos for the proper number of chromosomes, which is called euploidy. An abnormal number of chromosomes (too many or too few) is known as aneuploidy and can result in birth defects such as Down syndrome. In evaluating for proper chromosome numbers, PGS tests for many chromosome problems in one test. For couples with a known risk of heritable, debilitating diseases (often discovered through detailed family history evaluation by a trained geneticist), genetic testing can lower the risk of passing that disorder on to their child. Genetic testing can also help increase the chances of a healthy pregnancy by screening for potential genetic problems that might negatively affect pregnancy and birth.
