PGD stands for preimplantation genetic testing/ Diagnosis, it comprises a group of genetic assays used to evaluate the embryo before transferring it to the uterus. Preimplantation genetic testing is a highly modified technique which is used to identify genetic defects in embryo created through the IVF in vitro fertilization before pregnancy, preimplantation genetic diagnosis refers specially when one or both genetic parents has any known genetic abnormality and the testing is generally performed on an embryo to determine if the embryo also carries any genetic abnormality. In this procedure the embryos can be tested for abnormal chromosomes before they are transferred to uterus, Along with this preimplantation genetic screening also referred as PGS is a technique where the embryo from the presumed chromosomally normal genetic parents are screen for aneuploidy.
Because only the uninfected embryos are transferred to the uterus for implantation preimplantation genetic testing provides alternative to current post conception diagnostic procedure that is chronic villus sampling or amniocentesis. Preimplantation genetic testing aur diagnosis is the only option available that is used to avoid high risk of having children with any genetic disorder prior to implantation, PGD is an attractive means of preventing heritable genetic diseases thereby it helps to eliminate the dilemma of pregnancy termination following unfavourable prenatal diagnosis.
Common diseases diagnosed through PGD:-
- BRAC1 BRAC 2 genetic mutation
- Hemophilia A
- Sickle cell Anemia
- Myotonic dystrophy
- Fragile x syndrome
- Duchenne muscular dystrophy (DMD)
- Cystic fibrosis (CF)
- Human immunodeficiency virus(HIV)
- Tay Sachs disease
Indications of PGD
- Advanced maternal age (>35 years)
- Unexplained fertility
- Male factors
- Known genetic causes
- Recurrent miscarriage
- Repeated IVF
Classification of PGD Genetic Testing:-
Basically there are three types of preimplantation genetic testing depend on defects evaluated-
2) PGT-M - in this monogenic diseases can be evaluated in the embryo, monogenic disorders are basically caused by single gene mutation.
3) PGT-SR - average structural abnormality into the chromosome is taken inside this (translocation, inversions, duplications insertions, deletions)
How is PGD performed:-
In This procedure one or more than one cells are taken from the embryo and send for genetic testing while the embryo is already growing in the IVF laboratory, in this there are different stages of testing which is done using different techniques these techniques include fluorescent in situ hybridization (FISH), microarray and single nucleotide polymorphism (SNP). More the techniques are constantly evolving and are changing to work more accurately and it will be easier to access.
Benefits of Preimplantation genetic testing:-
As Preimplantation genetic testing is done in the chromosomes it can help to identify any diseases linked to chromosome genetics or hereditary diseases, chromosome diseases are one of the most common and major cause of infertility and maternal age related reduced fertility potential, preimplantation genetic testing can help to shorten the time to a viable pregnancy by reducing the need of multiple in vitro fertilization cycles. It can also help to reduce the miscarriage risk independent of maternal age.
- Helps to identify and avoid fertilisation embryos that carry genetic diseases and conditions
- Identify the sex of the embryo and select which sex to implant.
- Helps to allow intended parents who are carriers of genetic disorders to conceive with significantly lower risk of passing that genetic disorders to the children
- Helps to improve the chances of successful pregnancy by transferring strongest and the best embryos in the uterus.
Risks of treatment:-
Generally the risk involved in in implantation genetic technique are similar to conventional in vitro fertilization IVF-
- Fertility drug reaction which includes hot flashes headaches restlessness feeling down or irritable the symptoms of this usually disappears after a short time.
- Multiple pregnancy is a risk of complication in which there are higher chances of twins or multiples
- Pelvic infections
- Ectopic pregnancy ab pregnancy is another risk factor in which the pregnancy development is in the fallopian tube instead of the womb
- Miscarriage there are risk of miscarriage after IVF is no higher or lower then after a neutral conception.
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