◆What is niPGT-A?
niPGT-A (niPGS) is the latest non-invasive testing technique in preimplantation screening, offering a fertilized egg (embryo) friendly approach without the need for TE cell collection.
◆niPGT-A (niPGS) Features
Because niPGT-A does not involve the collection of TE cells and is non-invasive to the fertilized egg (embryo), it can test for chromosomal abnormalities without damaging the embryo more than conventional PGT-A (PGS). Specifically, the procedure involves collecting the culture medium from a blastocyst that has grown on the sixth or seventh day after fertilization, extracting and amplifying DNA from it, and analyzing it by NGS. The blastocysts are cryopreserved until the test results are obtained.
◆Advantages and Disadvantages
- No damage to the embryo
No damage to the embryo because the culture medium, which is normally discarded, is used.
- Preliminary confirmation of chromosomal aberrations
The ability to pre-screen for chromosomal aberrations in embryos for transfer reduces the miscarriage rate and shortens treatment time.
- Reduced risk of congenital disease
This may avoid difficult decisions during pregnancy because it reduces the risk of congenital disease.
- Improved embryo grading
Lower grade embryos can be tested than in the past, and chromosomal abnormalities can be examined prior to transfer.
- Improved pregnancy rate and reduced miscarriage rate
It is expected that the probability of successful transplantation and pregnancy rate will be improved and the miscarriage rate will be reduced.
- Gender Identification
The gender can be known if desired.
- No validity for miscarriages not due to chromosomal aneuploidy
Even if the test is correctly established, it is not valid for miscarriages not due to chromosomal aneuploidy.
◆Method of Examination
①Egg retrieval, ICSI, and blastocyst culture: Egg retrieval, ICSI, and blastocyst culture are used to produce embryos.
②TE biopsy is performed to collect TE cells from blastocysts.
③E DNA extracted from cells is amplified using the PCR method.
Next generation sequencing (NGS): Amplified DNA is subjected to chromosomal analysis by next generation sequencing (NGS).
NGS analysis results show the number of autosomes (chromosomes 1 through 22) and sex chromosomes (X and Y chromosomes). The analysis results are plotted in a graph, with a blue line for cases with three chromosomes (trisomy) and a red line for cases with only one chromosome (monosomy).
Normally, there are two autosomes each, which plot in a straight line on the baseline if there are no chromosomal abnormalities.
As an example, the above test result has one chromosome 16 less, so excluding it from the implantation candidates is expected to have a positive effect on the implantation rate.
Example result: Monosomy16, [45,XX,-16].
As for the consistency of multiplicity between ICM biopsy or TE biopsy and the corresponding SCM of the same embryo, As of 2023, it is being debated around the world and no clear empirical results exist.
False positives/false negatives should always be considered.