Non-Invasive PGT-A: Part 3

In the last years there have been different attempts to overcome trophectoderm biopsy to diagnose the chromosomal content of the embryos. A non-invasive approach has been proposed that consist in the study of the embryo cell-free DNA (cfDNA) released by the embryo to the culture media during the latest stages of preimplantation development. After the first publications, several studies have compared the results of preimplantation genetic testing of aneuploidies (PGT-A) in trophectoderm (TE) biopsies with the results of the spent blastocyst media (SBM), to establish the concordance rates among both approaches. In these studies of non-invasive PGT-A (niPGT-A), the percentages of informative samples vary widely, likely as a consequence of the use of different methodologies and criteria used for result interpretation, urging the need for technical improvements before this new non-invasive technology can be clinically applied. In this presentation you will be provided with a critical appraisal of available scientific literature on niPGT, revisioning the strengths and limitations of the different scientific approaches employed to assess the performance of non-invasive preimplantation genetic testing.

In the last years there have been different attempts to overcome trophectoderm biopsy to diagnose the chromosomal content of the embryos. A non-invasive approach has been proposed that consist in the study of the embryo cell-free DNA (cfDNA) released by the embryo to the culture media during the latest stages of preimplantation development. After the first publications, several studies have compared the results of preimplantation genetic testing of aneuploidies (PGT-A) in trophectoderm (TE) biopsies with the results of the spent blastocyst media (SBM), to establish the concordance rates among both approaches. In these studies of non-invasive PGT-A (niPGT-A), the percentages of informative samples vary widely, likely reflecting the existence of mosaicism and/or presence of DNA from cumulus cells or polar bodies in the SBM, urging the need for technical improvements before this new non-invasive technology can be clinically applied.

More recently we have performed the interim analysis including 1,301 blastocysts obtained from 371 patients aged 20-44 years undergoing PGT-A and with TE biopsy and media collection on day 6. No previous assisted hatching or vitrification was allowed before media collection. Global concordance rates of the SBM with the corresponding TE biopsies were 78.2%. No significant differences were detected among centers ranging from 72.5% to 86.3%. A prioritization algorithm has been developed according to the concordance results observed and we suggest that an embryo prioritization system considering the euploidy rates in the SBM compared to the TE biopsy could offer a different perspective for patients and clinicians that do not want to undergo PGT-A, avoiding invasive embryo biopsy and decreased cost, potentially increasing accessibility for a wider patient population.

Preimplantation genetic testing (PGT) has been widely used by IVF centers and clinics, for screening genetic abnormality before embryo transplantation. Blastomere or trophectoderm cells are the common sources of the genetic material of the embryo tested. Due to the invasiveness of the embryonic biopsy for the conventional PGT, there have been concerns about the technical safety and long-term effects on embryos having not yet been revealed.

A new generation non-invasive or mini-invasive PGT techniques have now been developed and applied in clinical studies and trials in the last five years. The blastocyst culture medium and blastocoele fluid were found to contain embryonic cfDNA and can be used as an alternative source for PGT. Owing the advancement of single-cell whole genome amplification methods and next generation sequencing, the ultra-low picrogram level of genomic DNA can be detected and sequenced for screening genetic abnormality at chromosomal and even single-base level.

Owing to Yikon’s patented whole genome amplification technology MALBAC, the non-invasive chromosome screening (NICS) for human embryo has been developed and the global first NICS baby was born 2016. The single-centre pilot clinical study of NICS obtained an ongoing pregnancy rate of 58% and reported 27 normal live births. With a continues development of NICS, it has now equipped with a machine learning-guided analysis system based on data collected from 345 paired blastocyst culture medium and whole blastocyst samples to predict euploidy in blastocyst IVF embryos. The new AI-based NICS validated in a blinded prospective observational study with 160 patients. We observed a significant increase in the ongoing pregnancy rate in A- versus Cgrade embryos and B- versus C-grade embryos, and a significant decrease in miscarriage rates compared to the morphological grading system. We hope IVF patients would benefit from the use of NICS technology with improved clinical outcomes.