One cell is removed from an 8-celled embryo for genetic testing.
Genetic Testing Of Embryos
• What Is Pre-Implantation Genetic Diagnosis?
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Assisted Reproductive Technology
|Terminology: Pre-implantation genetic diagnosis (PGD) is also known as pre-implantation genetic testing (PGT).
What Is Pre-Implantation Genetic Diagnosis?
Pre-implantation genetic diagnosis (PGD) is a service offered by some fertility clinics to couples undergoing IVF. PGD makes it possible to check an embryo for chromosome abnormalities and gender before implanting in the mother. If you carry a genetic disease or gender-linked disease a counselor may recommend having your embryo's chromosomes assessed before having them transferred to your womb. PGD can be done to check the embryo has the correct amount of genes or to check for the presence of a certain gene. In most cases both partners have been genetically screened and one or both have been identified to be carriers of genetic abnormalities.
PGD can test for:-
PGD may be recommended where either or both parents carry a genetic abnormality and doctors want to test for this disorder in the embryo before it is implanted. Preimplantation genetic screening (PGS) is where both parents are assumed to be chromosomally normal, but they want the embryo screened for abnormalities, just to be safe (the mother may be aged over 35 and is worried about the risk of Down syndrome for example). Both tests are an alternative to genetic testing during pregnancy, where procedures such as amniocentesis or chorionic villus sampling (CVS) are used. Of course testing before the embryo is implanted is better because it eliminates the dilemma of a termination if the prenatal test is positive.
Using IVF technology, one cell called a blastomere is removed from an 8-celled embryo. The cell is then tested for number of chromosomes and specific genetic defects. PGD is time intensive and it is estimated that up to 10 percent of diagnoses are not correct. This is because only one cell is being tested, compared to hundreds via an amniocentesis test. It is further complicated by the fact that some embryos have something called mosaicism. This means that not all cells have the same number of chromosomes. So while the cell being tested may be normal, all the other cells might be abnormal (or vice versa). Only certain fertility clinics are equipped to carry out PGD. The test itself is performed by an embryologist.
The PGD procedure:
• Is performed before implantation so reduces the need for amniocentesis in pregnancy.
• It does not test for all chromosome abnormalities, just the most common ones. It misses 10 to 15 percent of abnormalities.
Those worried about PGD testing claim it allows couples to have designer babies. PGD testing allows parents to choose the sex of their baby and to select healthy, non-genetically diseased embryos. But where does it end? Many ethicists worry parents in the near-future will be able to design their perfect baby, by selecting physical appearance of their child, including eye and hair color and height. Inevitably it is feared that the rich (those that can afford the procedure) will become like some super race of America’s top models, while the rest of the population become stigmatized for their ordinary or sub-standard physical appearance. Another concern is that PGD leads to the destruction of rejected embryos, but in practice, not that many are destroyed.
The average cost of PGD is $3,200 in the United States. The fee for this optional service will be tagged on to your overall cost for IVF treatment. Most insurance companies do not cover the costs.
|Related Articles on ART Procedures
For more information, see the following:
• Genetic testing before pregnancy: Assessing your risk as parents.
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