In much the same way that doctors screen for fetal issues via amniocentesis, preimplantation genetic testing is used to screen embryos created through in vitro fertilization (IVF) for genetic abnormalities. But it’s performed on embryos before they’re implanted in the uterus.
When one or both parents have a known genetic abnormality, preimplantation genetic diagnosis (PGD) testing is performed on an embryo to determine if it carries the same genetic abnormality. The providers at Fertility & Genetics recommend a screening method called PGD plus Parental Support for greater accuracy.
Preimplantation genetic screening (PGS) tests embryos from presumed chromosomally normal genetic parents for aneuploidy, a condition in which the embryo has missing or extra chromosomes.
For couples who pursue IVF, PGS offers embryo screening to improve the chance of achieving a healthy pregnancy. Screening for the number of chromosomes allows for the selection and transfer of embryos most likely to have the correct chromosome number. These embryos are more likely to implant and are much less likely to miscarry.
Any couple can have an embryo with aneuploidy, but some are at higher risk. Issues that put the embryo at higher risk for aneuploidy include:
The biggest problem with PGD is the chance of misdiagnosis. PGD plus Parental Support increases the accuracy rate to 99 percent, making this method the most accurate PGD test available. Accuracy is increased by evaluating 35 small sections of DNA, called markers, while other PGD methods typically evaluate two to six markers.
Also, all embryo samples are matched to DNA samples taken from the parents to confirm that the DNA being tested is from the embryo. The entire chromosome carrying the gene mutation is evaluated to make sure there are exactly two copies before making a diagnosis on gene status. Every Parental Support PGD test includes Trisomy 21 screening to reduce the chance of Down syndrome.
Preimplantation genetic testing requires embryo biopsy, the removal of either a single or a small number of cells from a growing embryo. The biopsy procedure can be performed on day three after egg retrieval or, more commonly, on day five or six, when embryos reach the blastocyst stage of development.
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