Pre-implantation Genetic Testing (PGT)

What is Pre-implantation genetic testing?

Pre-implantation genetic testing is an early form of pre-natal genetic diagnosis, which is usually carried out on embryos prior to embryo transfer to determine genetic abnormalities. Those embryos which are genetically normal will be used for embryo transfer procedure.

What is the purpose of Pre-implantation genetic testing?

PGT helps to reduce the risk of miscarriage, a complication related to pregnancy failure, prevent undesired genetic traits and thereby improving the chances of a viable pregnancy.

PGT includes:

  • PGT-A (for aneuploidies): Used to check whether the embryos has correct number of chromosomes.

Indications:

  • Advanced maternal age
  • Multiple previous failed IVF attempts
  • Repeated miscarriages
  • Previous history of pregnancy with chromosomal abnormality
  • Previous history of child born with chromosomal abnormality
  • PGT-M (for monogenic/single gene defect): used to check for a specific gene defect or for inherited mutations which is carried by one or both the biological parent.

Indications:

  • Carrier of single gene disorders like:
    • Beta-thalassemia
    • Cancer predisposition genes (BRCA1/2, Lynch Syndrome, and others)
    • Cystic fibrosis
    • Duchenne muscular dystrophy
    • Fragile X syndrome
    • Huntington disease
    • Retinoblastoma
    • Sickle cell anemia
    • Tay-Sach disease
  • One or both partners or family history of heritable genetic disorders
  • One or both partners is a carrier of chromosomal abnormality
  • Couples who have child/children affected by a single gene disorder.
  • PGT-SR (for chromosomal structural rearrangements): used to identify balanced translocation, or deletion/duplication. Newer technologies allows to distinguish normal non-carrier embryos from balanced carriers.

How is the Pre-implantation testing procedure carried out?

Pre-implantation genetic testing requires the couple or individual to undergo egg collection followed by Intra-cytoplasmic sperm injection procedure (ICSI).   

                                                                            
Stages of PGT:

Pre Implantation Genetic Process - Ova Fertility and Women Care
Pre Implantation Genetic Testing - Ova Fertility and Women Care

Image Source: https://www.invitra.com/en/preimplantation-genetic-diagnosis-pgd/

What are the limitations of Pre-implantation genetic testing?

    • The test results are not 100% accurate. Hence pre-natal genetic screening might be recommended.
    • Mosaic embryos
    • PGT cannot detect all abnormalities or birth defects and therefore does not guarantee a healthy live pregnancy.

                                                                                

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