Pre-implantation genetic testing (PGT)

Pre-implantation genetic testing is a screening test which is a part of invitro fertilization (IVF) / intra cytoplasmic sperm injection (ICSI). Most of the embryos that are formed, are genetically abnormal, which may result in implantation failure, pregnancy with abortion or pregnancy with birth defects in the baby. Pre-implantation genetic testing involves genetic testing of embryos formed by IVF/ICSI.

Who requires Pre-implantation genetic testing?

Pre-implantation genetic testing is advised for couples:

  • Who have had a previous pregnancy with genetic disorder
  • Who have had recurrent miscarriages
  • Who have had multiple IVF failures/recurrent implantation failures
  • Woman older than 38 yrs
  • Who have a family history of genetic disorder
How is the test performed?

The test involves removing few cells from the outer layer of Day 5 embryo (blastocyst), known as trophectoderm and sending those cells to conduct genetic testing on DNA. The biopsy removes 3-10 cells without disturbing the inner cell mass of the embryo which forms the future baby. There is a minimal risk of damaging the embryos while doing the test. The embryos are cryopreserved until the results are available. The results will be available in 7-21 days. These tests are not 100 % guaranteed but they do reduce the risk.

What are the types of Pre-implantation genetic testing?

There are three types of Pre-implantation genetic testing:

  • PGT-A (Pre-implantation genetic testing-Aneuploidy): This type of genetic testing screens abnormal number of chromosomes. The human cells contain 23 pairs of chromosomes. Any reduction or addition in the chromosome number will lead to abnormal number of chromosomes known as anueploidy. These embryos are not healthy and they either do not implant or causes pregnancy losses. Hence, finding an embryo with normal number of chromosomes contributes to a higher success rate.
  • PGT-M (Pre-implantation genetic testing-monogenic disease): PGT-M identifies specific gene disorders that one or both the parents is known to carry. It identifies diseases like sickle cell anemia, thalassemia, BRCA 1 & BRCA 2, etc.
  • PGT- SR (PGT for chromosomal structural rearrangement): PGT- SR is done on embryos of couples known to have chromosomal structural rearrangements like translocation or inversion like Robertsonion translocation.