Pre-implantation Genetic Testing
Pre-implantation genetic testing (PGT) consists of a group of genetic assays used to evaluate embryos before transfer to the uterus. PGT can be performed with either cytogenetic or molecular techniques to test for single gene disorders, aneuploidy, or structural chromosomal abnormalities associated with inherited diseases and cancer syndromes.
The three main types preimplantation genes screening-aneuploidy (PGT–A), Preimplantation genetic screening–monogenic (PGT–M) and Preimplantation genetic testing to structural rearrangements are the preimplantation genetic tests-structural rearrangement (PGT–SR). Each has been shown to have clinical utility.
Aneuploidy is a condition that causes abnormal numbers of chromosomes to be present in an embryo. It is the leading cause of fertility problems and pregnancy losses. These chromosomal flaws can include deletions (duplications), or amplifications that affect chromosome pairs not found in normal embryos. These chromosomal flaws may increase the chance of miscarriage or chromosomal disorders like Down syndrome. Down syndrome occurs when a baby is born with an extra copy 21 of chromosome 11.
Aneuploidy in embryos is unlikely to implant in uterus. It can lead to multiple pregnancy or birth defects. They are more at risk of spontaneous death and have a lower rate for live births than other embryos.
Aeuploidy may also be difficult in early pregnancy due to mosaicism (when the chromosomes are not distributed evenly). Preimplantation genetic testing may show false-positive results if there is mosaicism.
Preimplantation genetic testing should not be performed without considering the individual risks, reproductive goals, and preferences of the patient. Before she undergoes preimplantation genetic testing, it is important to discuss these issues with her medical team as well as her partner.
pgd in Tampa is the most commonly used type of preimplantation genetic testing and screens for inherited single-gene disorders such as Huntington disease, cystic fibrosis, fragile X syndrome, and hereditary breast and ovarian cancer. It also tests for other disorders that are not caused by a single gene, such as hereditary syphilis and hereditary leukemia.
It is not capable of diagnosing certain genetic disorders like microdeletions and microscopic duplications. For these conditions, an amniocentesis must be performed to provide a more definitive diagnosis.
PGT-M is not shown to increase fertility or reduce the risk of pregnancy in patients who have failed IVF cycles repeatedly. It is also unknown if this procedure is cost-effective.
Embryos with chromosome abnormalities are rarely able to survive in the uterus and can lead to a variety of health problems in the child, including birth defects and intellectual disabilities. Preimplantation genetic testing for aneuploidy should be reserved for women over 35 years old with no previous failed fertility treatments or high egg quality, according to current American Society of Reproductive Medicine guidelines.
Although there are more options for testing, questions remain about how to best use preimplantation genetic testing. Future research is needed for understanding the clinical utility of the method and the subset patients that may benefit from using it. Also, to investigate mosaicism and to determine residual aneuploidy risk in screened eggs.