PGT and NICS – similarities and differences: invasive and non-invasive genetic testing of embryos

Modern reproductive medicine allows embryos formed by in vitro fertilization to be genetically analyzed before embryo transfer. The goal is to get additional information about the genetic and chromosomal status of the embryo and, in certain cases, to assist in the selection of an embryo for transfer.

In this context, the terms PGT are often encountered and NICS, i.e. invasive and non-invasive approaches to genetics material of the embryo.

But what exactly do these terms mean and how do they differ?

What is PGT?

PGT – Preimplantation Genetic Testing, ie preimplantation genetic testing, is genetic testing that is done on embryos obtained through IVF procedure.

Depending on what is being examined, there are different ones types of PGT:

• PGT-A – testing for abnormal number of chromosomes, i.e. aneuploidy;
• PGT-M – testing for specific monogenic or hereditary diseases;
• PGT-SR – testing for structural chromosomal changes.

PGT, therefore, is not a single test, but a group of genetic tests with different purposes.

How is classic, invasive PGT done?

In the traditional approach, when the embryo reaches blastocyst stage, the embryologist takes a small number of cells from the outer layer of the embryo – the trophectoderm.

This is called an embryo biopsy.

The cells are sent for genetic analysis, while the embryo is usually frozen and that's it he is waiting for the result before making a decision on the transfer.

This method allows direct access to cells of the embryo and today represents established protocol for PGT in clinical practice. However, like any laboratory procedure, it requires a high level of expertise and careful implementation.

What is NICS?

NICS – Non-Invasive Chromosome Screening, ie non-invasive chromosome screening refers to a protocol in which no cells are taken directly from the embryo.

Instead, it analyzes genetic material that the embryo releases it in medium for cultivation in which it develops.

During development, the embryo releases fragments of DNA in the medium. With modern molecular techniques, these fragments can be analyzed and get information about the chromosomal status of the embryo.

This is exactly the basis of the concept of non-invasive PGT, which is also found in the scientific literature as niPGT.

PGT and NICS – what do they have in common?

Although the approach is different, the goal is similar: to obtain information about the geneticcomposition of the embryo before its transfer.

In both approaches:

• everything works with embryos formed through IVF;
• everything analyze DNA originating from the embryo;
• analysis is performed using state-of-the-art NGS (Next - Generation Sequencing) technology
• can to examine chromosomal status, especially in the context of PGT-A;
• the results may assist in the embryo selection process for transfer, depending from the specific case and the medical indication.

The main difference is where the genetic material is obtained from.

Key Difference: Invasive vs. Non-Invasive

In classical PGT, the genetic material is obtained through a biopsy of cells from the embryo.

With NICS, the idea is to analyze the DNA present in the culture medium, without taking cells directly from the embryo.

Therefore the non-invasive approach has a potential advantage: they are not do a biopsy of the embryo.

However, this is where one of the biggest challenges lies.

The amount of DNA in the culture medium can be very small, and the sample can to contain DNA from other sources. Additionally, the result may be below influence of conditions for culture, the way of collection of the medium and other laboratory factors.

Is NICS a complete replacement for PGT?

It doesn't necessarily mean.

Although non-invasive genetic testing is one of the interesting ones areas in the development of reproductive genetics, accuracy and clinical applicability of these methods are still subject to researchand advancement.

Scientific studies show varying levels of compliance among the results obtained from the medium for culture and biopsy results, which indicates that methodology and laboratory conditions have a significant impact.

Therefore, the non-invasive approach should be seen as a technology with great potential, but not automatically better or fully equivalent substitute for established methods.

What does the future hold?

The idea of genetic testing without direct intervention on the embryo is extremely attractive.

In the future, further development of technology may ovozmoži ušte poprecizno analiziranje na genetskiot materijal koj embrionot go releases in the medium for cultivation.

The scientific community is actively working to improve the accuracy, standardization of laboratory protocols and validation of clinical benefit from these methods. Currently, however, noninvasive PGT remains an area which is still developing.

Conclusion

PGT and NICS have the same broad objective – to provide genetic information about the embryo before the transfer, but that information is coming in a different way.

Biopsy PGT collects cells directly from the embryo for genetic analysis, while NICS tries to use them the genetic traces that the embryo leaves in the culture medium.

That is why the future of reproductive genetics is heading towards methods that will provide as much information with as little intervention as possible on the embryo.

But as with any medical technology, the most important the accuracy of the results, the scientific support and the correctness remain interpretation in the context of the specific patient and IVF cycle.