Pre-implantation genetic Diagnosis (PGD)
Pre-implantation genetic Diagnosis (PGD) is the detection of genetic defects or disease in embryos derived from In Vitro fertilization (IVF) after which the unaffected embryos are transferred into the uterus.The aim of PGD as a form of early prenatal diagnosis is avoidance through selection of embryos.
In this way a couple at risk of having a child with a genetic disorder can initiate a pregnancy knowing that the child is not affected.
PGD aims to eliminate the risk for genetically disadvantaged couples, eliminate the period of time for prenatal diagnosis and subsequent psychological trauma the couple may face with the decision of a selective abortion.
PGD may be a solution to couples unwilling to undergo voluntary abortion for ethical or religious reasons.
What's involved?
Patients undergoing PGD are advised to go through genetic counseling before, initiating IVF treatment.
The PGD cycle is exactly the same as for IVF patients, although all patients undergo ICSI.
Usually on the third day post-insemination when the embryo is at the 6-8-cell stage one or two blastomeres (embryonic cells) are sampled from each embryo.
The biopsied cells are genetically analysed, and the embryos found to be free of a particular disease can then be transferred.
Embryo biopsy, is it safe?
Research has shown that the biopsy has no detrimental effect on the development of the embryo, and all children born after PGD have been healthy.
What are the disadvantages?
The success of PGD is limited is the restraints of IVF. While patients may favor pre-implantation genetic diagnosis, they must come to terms that there is no guarantee of pregnancy after a successful screening of embryos and subsequent embryo transfer.
Because many good quality embryos are needed for biopsy and some embryos are subsequently "selected out" after diagnosis , many oocytes are needed to be recruited
- This may mean cancellation of a poor superovulation cycle.
- The suitability of older patients is debatable.
There is a small risk of misdiagnosis and in most centers prenatal diagnosis is still recommended.
Pre-implantation Genetic Screening
Chromosomal abnormality has been found in embryos generated after super ovulation and IVF, which might account for low pregnancy rates in IVF.
An increase in chromosomal abnormality in older women might represent the cause of failure in older patients.
The objective of screening Pre-implantation embryos is to increase pregnancy rates after IVF and reduce abortion rate by selecting the healthiest embryos. Screening for chromosomal abnormalities by the method FISH may be an additional selection criteria, other than morphology and developmental status.
Chromosomes abnormalities frequently associated with recurrent abortions, as well as the chromosome imbalances such as that which causes downs syndrome can be screened for in the embryo before transfer.
