Next Generation Sequencing or NGS is a new technology for comprehensive chromosome testing of IVF embryos. Next Generation Sequencing for PGD is likely going to replace other technologies as the predominant method for preimplantation genetic screening (PGS) due to lower cost and reduced errors.
Next Generation Sequencing involves Whole Genome Sequencing (WGS), Whole Exome Sequencing (WES) and Targeted Regional Sequencing.
Successful In Vitro Fertilisation (IVF) is based partially on successful selection and transfer of healthy, viable embryos. Initially, embryo selection was performed by examination of the embryo appearance under a microscope. This is known as morphology assessment. However, unfortunately many embryos with a normal appearance under the microscope might not be able to produce a live born baby eventually.
We now know that many embryos might appear to be normal under microscope, but actually have abnormalities in the number of chromosomes (aneuploidy). These abnormalities are the leading cause of IVF implantation failure and spontaneous miscarriage.
One possible reason is that the results obtained from FISH were limited to only few of the 23 total chromosomes in human beings. We now know that abnormalities may occur in any of the 23 chromosomes. This led to the use of more robust, automated technologies which were capable of looking at all 23 pairs of chromosomes.
NGS-based pre-implantation genetic screening is the latest technique which makes it possible to detect an abnormal number of chromosomes based on an examination of a single cell. Recent studies indicate that PGS improves chances for pregnancy by 55-70% in many cases.
Potential advantages using NGS are:
- Reduced cost
- Enhanced detection of structural abnormalities such as chromosomes with missing or duplicate segments
- Better ability to detect when an embryo may have cells with differing results (mosaicism)
- Reduction of human errors by increasing use of automation
How does NGS-based PGS work?
Embryo will be cultured for 3 or 5 days. Following that is embryo biopsy. A cell will be removed from each good quality day-3 embryo (6-8cell), or, 3-5 cells from a blastocyst.
Genetic test will be performed on a single cell / trophectoderm cells for screening the chromosomes aneuploidy of all 46 chromosomes.
- Consultation with doctor to see whether you need NGS-based PGS
- Signing the consent form
- Performing embryo biopsy on Day 5 blastocysts and extract the cells
- Delivering the samples to the laboratory and the result could be obtained within 5 to 10 working days
- Doctor implanting the normal embryos with reference from the report
Who would benefit from NGS?
- 35 years old or above
- Repeated miscarriage or pregnancy loss
- Repeated implantation failure
- With family history of chromosomal abnormalities
- Avoid chromosomal aneuploidies