PRE IMPLANTATION GENETIC TESTING
Genetics contributes to 10% of infertility issues and recurrent pregnancy losses among couples trying to conceive and the risk increases especially in cases of advanced maternal age. Therefore, genetic testing has the potential to help many couples in their quest to have a family. PGT is an early form of prenatal genetic diagnosis wherein embryos are screened for genetic diseases and chromosomal disorders.
The various kinds of PGT are:
PGT-A: Pre-implantation Genetic Testing for Aneuploidies
This is done to check for an extra or missing copy of a chromosome as it can lead to improper development and functioning. Therefore, embryos with incorrect amount of genetic material are called aneuploid, while the ones with correct amount of genetic material are called euploid.Such abnormalities can happen by chance and are not typically inherited from a parent or donor.
PGT-M: Pre-Implantation Genetic Testing for Monogenic/Single gene defect
This involves testing the embryos for any monogenic disorders like sickle cell anemia, Huntington’s disease, Fragile X syndrome etc when either woman is a carrier of an X-linked condition or when an individual and their partner or donor are both carriers of some autosomal recessive condition.
PGT-SR: Pre-Implantation Genetic Testing for Chromosomal Structural Rearrangements
This tests people with chromosomal rearrangement such as translocation or inversion as these people are at risk of producing embryos with missing or extra pieces of chromosome.
What are the indications for PGT?
1. Advanced Maternal age(35yrs or older)
2. Recurrent miscarriage
3. Multiple failed IVF cycles
4. Previous offspring with chromosomal abnormalities
5. Genetic disorders wherein, either or both of the parents are carriers or affected
How is PGT performed?
All the three types of PGT are performed in a similar fashion:
1) The patient goes through egg retrieval followed by an IVF cycle
2) The embryos are then monitored in the laboratory from D0 to D5, being referred to as Cleavage stage embryos till D3 and Blastocyst on D5
3) The embryologist and physician then decide the best day for embryo biopsy, taking into consideration, the number of oocytes retrieved, developmental status of embryos, ET strategy and personal experience
4) Then a small number of cells are biopsied(removed)from each embryo and are sent to an outside laboratory for PGT. These cells are expected to be representative of the entire embryo
5) The embryos are then frozen while PGT is performed 6) Finally, embryos with no genetic abnormalities are selected, thawed and transferred into the woman’s uterus
Frequently asked questions
Q1. How long does it take for the PGT results to come?
Ans- Once the lab receives the embryo biopsy sample and the payment, results can usually be expected within a span of 7-10 days
Q2. Do normal PGT results completely eliminate the risk of any genetic condition in the embryo?
Ans- No, PGT screens either for certain chromosomal abnormalities or one specific genetic condition. But, every pregnancy has an approximately 3-5% chance of an offspring with a genetic condition or birth defect and there is no genetic test to eliminate or rule out all diseases or birth defects. Therefore, regardless of the screening, there is always risk for a child to have medical issues, whatsoever.
Terms often confused
|Current Name||New Name|
|PGS (Preimplantation Genetic Screening)||PGT-A (Preimplantation Genetic Testing for Aneuploidies)|
|PGD (Preimplantation Genetic Diagnosis) for Single Gene Disorders||PGT-M (Preimplantation Genetic Testing for Monogenic/Single Gene Defects)|
|PGD (Preimplantation Genetic Diagnosis) for Chromosomal Rearrangements||PGT-SR (Preimplantation Genetic Testing for Chromosomal Structural Rearrangements)|