What is preimplantation genetic testing (PGT)?
Embryo morphology is not accurate to detect the most viable embryos. One of the main reasons why good quality embryos fail to implant is because of their genetic status. The percentage of abnormal genetic embryos during IVF treatment is relatively high when patients are over 38 years (around 50-60%).
Thus, PGS is used to detect chromosomal abnormalities and chromosomal rearrangements (translocations, inversions, deletions, etc). Embryos that have a normal number of chromosomes are more likely to result in a viable pregnancy. PGD is a technique, which enables couples with a particular inherited diseases in their family to avoid passing it on to their children. PGD is performed on embryo to determine if it has also inherited the genetic or chromosomal abnormality.
Preimplantation genetic testing of embryos is generally divided into:
Preimplantation genetic diagnosis (PGD)
One or more cells from an embryo are tested for the presence of a gene or genes that may harm the embryo and developing child, correct number of chromosomes, and translocation of a piece (or more) of chromosome from one to another chromosome.
Preimplantation genetic screening (PGS) is used to detect chromosomal abnormalities and chromosomal rearrangements (translocations, inversions, deletions, etc) and to test for the number of chromosomes. This is also known as aneuploidy screening.
What are advantages of PGT?
It is an alternative to
- prenatal diagnostic testing: Couples avoid the stress during pregnancy associated with diagnosis.
- termination of pregnancy: when prenatal testing (amniocentesis or chorionic villus tests) reveals a genetic abnormality
The opportunity to conceive a pregnancy that is biologically the parents’ own and yet unaffected by a genetic condition in the family.
What are disadvantages of PGT?
The process of IVF and PGD poses some risks to the woman and the embryo:
- Health risks of the IVF cycle
- An embryo may not develop after fertilization of an egg
- Not all embryos will be suitable for biopsy
- The embryo may not develop after biopsy
- There may not be any unaffected embryos available for transfer
- Test results may be inconclusive
- Results are not 100% accurate
- No pregnancy is achieved, even after the transfer of an unaffected embryo
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