Pre-implantation Genetic Testing

Introduction

Pre-implantation Genetic Testing (PGT) is a test performed on embryo(s) to identify single gene disorders or chromosomal abnormalities.

Pre-implantation Genetic Testing for Aneuploidy (PGT-A) uses complete chromosome studies to evaluate the total number of chromosomes in a single cell and determines any gain or loss of chromosomes.

Pre-implantation Genetic Testing for monogenic defects (PGT-M) is used to screen for monogenic disorders. Moreover, Pre-implantation Genetic Testing for structural rearrangement (PGT-SR) is used to screen for chromosomal rearrangements such as translocation or inversion. These screening tests prevent transfer of embryo(s) carrying that particular monogenic disorder and/or structural rearrangement, and avoid the need for termination of pregnancy related to that disease.

PGT-A

PGT-A involves screening the embryo for normal chromosome copy number. The main indications for the use of PGT-A in IVF treatments include advanced maternal age (AMA), repeated implantation failure, and recurrent pregnancy loss (RPL). It is well known that the rate of chromosome abnormalities is higher in patients with AMA and RPL. Also, PGT-A has been used in women with previous trisomic conceptions; partners with severe sperm defects and improve implantation in those with repeated implantation failure*.

*Please note that these are yet to be confirmed by randomized controlled trials.

PGT-M

PGT-M involves removing a few cells from an IVF /ICSI embryo(s) to test for a specific genetic condition before transferring the embryo to the uterus.

PGT-M for inherited genetic diseases can clearly benefit couples that carry a gene for a serious medical condition likely to affect their future children. It avoids selective pregnancy termination due to the inheritance of the maternal or paternal diseases.

PGT-SR

PGT-SR can benefit patients that are carriers of a chromosomal arrangement called a balanced translocation. Embryos from these couples have a high percentage of chromosomal abnormalities. These embryos are at very high risk for miscarriage or could result in the birth of a child with birth defects. By having IVF aneuploidy screening and transfer of chromosomally normal embryos, the risk for miscarriage and birth defects is greatly reduced.

How is PGT carried out

At day 5/6 of development, the blastocyst has over a hundred cells and removing 4-8 cells has only a small impact. The biopsied embryo(s) will be cryopreserved while awaiting test outcome. Depending on complexity, the results will be available within 2-4 weeks.

Who may benefit from PGT?

In general, there are 5 main groups of patients that may benefit from PGT:

• IVF in advanced female age - 35 years old / above or older
• Patients that have had recurrent miscarriages
• Repeated IVF failure
• Carrier of inherited genetic diseases
• Carriers of chromosomal translocations