A successful round of IVF is largely based on the correct selection and transference of viable and healthy embryo. Long back, the embryos were examined under the microscope for their appearance. Unfortunately, even such normal looking embryos had abnormalities specifically in the number of chromosomes known as aneuploidy. This resulted in failure of IVF implantation and spontaneous miscarriage.
With the advancement of science, we now have a new technology for Preimplantation Genetic Testing (PGT) known as Next Generation Sequencing or NGS. The scientists screen all 24 chromosomes in a growing embryo and choose to transfer only those embryos that have a healthy profile.
A few cells are taken from the developing embryo for testing. NGS amplifies the DNA from the cell’s nucleus to a thousand times and then uses to the sequencing technology to tally the number of copies of every single chromosome present in the cell. The scientists are thus able to correctly detect chromosomal errors. This allows the transfer of only a healthy embryo with a standard chromosome profile thereby enhancing the chance of a successful conception.
The biopsy for the cell extraction is mostly conducted on Day 5 embryo.
In the initial days of PGT, a technology known as Fluorescence in situ Hybridization (FISH) was employed. In this technology, a single cell was extracted at 8 cell stage of a developing embryo. Initially thought to be promising and used widely for PGT, it was made obsolete when the results were compared in large scale studies and no improvement was found in the chance of live birth. One major reason for its failure is that not all 23 chromosomes were analysed under this technology and the abnormalities could occur in any of the 23 chromosomes. Hence more comprehensive and automated technologies to cover all chromosomes were developed.
1. NGS is an advanced technology for enhanced detection of missing or duplicate segments of chromosomes and all other structural abnormalities.
2. It comes at a reduced cost.
3. Automation leads to reduction of human errors.
4. Increased ability of mosaicism detection (embryos possessing cells with differing results.
• Woman is of advanced age i.e., 38 years or older.
• She has a history of recurrent miscarriage.
• There have been repetitive failed IVF cycles such as consecutive implantation of 5 embryos without conception.
• There has been a previous chromosomally abnormal pregnancy such as Down Syndrome.
