Preimplantation genetic diagnosis (PGD) is a procedure which involves checking the genes or chromosomes of the embryos prior to implantation to help identify genetic defects within embryos. This helps to prevent certain genetic diseases or disorders from being passed on to the child before it is transferred.The embryos need to be tested in a lab prior to implantation into the womb, even if the partners have no fertility problems. Embryos which have been tested for genetic defects and are free of the condition will be transferred into womb and allows the identification and transfer of embryos free from aneuploidies to the mother.It also significantly increases pregnancy rates per transfer and reduces the time needed to achieve pregnancy.The embryos used in this procedure are usually created during the process of in vitro fertilization (IVF). With PGD testing, embryos created through IVF procedure are cultured in a laboratory for three days until they reach the 8-cell stage. At this stage a blastomere biopsy is done in which one or two of the blastomeres are removed by inserting a micropipette through the zona pellucida which surrounds the embryo.
It is significantly helpful when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality to the child.PGD provides an alternative to current postconception diagnostic procedures (i.e. chorionic villus sampling or amniocentesis) which are usually followed by the difficult decision of abortion if results are unfavorable. It is currently the only options available for avoiding a high risk of having a child affected with a genetic defect prior to implantation.It is consisted two steps, extraction of one or two cells from an IVF-produced embryo and application of the PGD test. PGD is important for doctor and embryology because it has advanced IVF results and allowed couples more opportunities to deliver a healthy child free from any potential genetic defects.
PGD was originally developed in the early 1980s as an alternative to post-implantation prenatal testing. The only other forms of prenatal diagnosis available involved chorionic villus sampling (CVS) and amniocentesis before this technology. Both of these technologies imply the examination of embryos during later stages of fetus development, when the embryo is already developing inside the mother womb. Couples who choose any of these tests must decide whether or not go for abortion if test results suggest positive for a particular genetic disease.In the initial stage of its development, PGD was used as a form of gender selection to avoid having a child with a sex-linked disease. Couples using PGD often choose to have only girls since males are prone to be affected by X-linked genetic disorders. PGD rapidly came to be used for three main groups of inherited disease, single-gene mutations such as cystic fibrosis and sickle cell anemia, chromosomal abnormalities such as Down syndrome and sex-linked disorders such as hemophilia.
Although PGD was originally thought to be a mechanism to dispose embryos affected by a particular genetic disease.Some couples have used PGD as a means of creating siblings who can provide transplants for their older siblings.