The aim of PGT-A is to genetically screen embryos to find those most likely to have the correct number of chromosomes, so that these euploid embryos are preferentially selected for transfer.
Since miscarriage rates increase exponentially beyond the age of 35, PGT-A is widely accepted as a means of identifying euploid embryos for women of advanced maternal age, to significantly improve their IVF outcome1.
PGT-A is also particularly useful in IVF programs working towards single embryo transfers (SETs)2,3. One of the current main goals of IVF worldwide is to move towards SET to minimise multiple pregnancies and their associated risks.
All couples undergoing IVF may be counselled and offered PGT-A as a means of embryo selection. This is particularly applicable for those couples with a large number of good quality embryos (based on morphology) available for transfer.
The Vitrolife EmbryoMap solution screens all 24 chromosomes in the human genome using next generation sequencing (NGS) technology to detect large chromosomal copy number variations (CNV) greater than 10Mbp across the whole genome, thereby providing an accurate and efficient view of the number of chromosomes in an embryo.
The Vitrolife EmbryoMap will be replacing the well-respected VeriSeq PGS solution internationally. The Vitrolife EmbryoMap solution has also undergone extensive validation studies and has shown to sensitivities and specificities both of 99.9%8.
The technology we use can detect:
The technology we use cannot detect:
Sample receipt at laboratory
Sample and patient information captured on the laboratory information management system.
Sample and library preparation.
Library pooling and sequencing.
Sequencing results are analysed and interpreted reporting.
Result reports are reviewed and authorised for release.
Authorised result reports are released to referring healthcare provider.
In the Next Biosciences laboratory, we report on mosaicism levels as:
The cut-offs between high- and low- level mosaicism as above are in keeping with current international guidelines9,10 and as new data becomes available these cut-offs may be reviewed and adjusted.
The latest research shows that some mosaic embryos can implant and result in an ongoing pregnancy and healthy live birth, but at lower success rates compared to euploids13,14. In general, low level mosaics have a better reproductive outcome compared to high level mosaics. One multicentre study showed that segmental mosaics, irrespective of the level of mosaicism, have the best reproductive outcome compared to whole chromosome mosaics11. It is, therefore, important that your PGT-A test of choice is validated to correctly identify both low level and segmental mosaics, the VeriSeq PGS Solution which is the precursor for the current Vitrolife EmbryoMap Solution utilised in the Next Biosciences laboratory has been shown to be superior in this regard13.
Studies have shown that mosaic embryos are less likely to implant and some have also demonstrated that mosaics can result in higher miscarriage rates compared to euploid embryos13. Therefore, transfer of euploid blastocysts should always be prioritised over mosaic embryos, as euploid embryos have the best reproductive outcome9,10.
Should transfer of a mosaic embryo be considered, this should be done together with a genetic counsellor whom has experience in this field. Next Biosciences has an in-house genetic counsellor who is able to support you and any of your patients whom may need to consider a mosaic embryo transfer.
If a mosaic embryo is transferred and a pregnancy is achieved, prenatal diagnosis should be discussed with a clinician with a good understanding of the benefits and limitations of all available options. While Non-Invasive Prenatal Testing (NIPT) may provide information early in a pregnancy (from 10 weeks), preference should be given to 24-chromosome NIPT methodology that includes the mosaic chromosome in question. It is important to understand that NIPT can only assess placental chromosome status. Amniocentesis is considered to be the most representative of the chromosomal complement of the fetus. All testing options should be discussed on a case-by-case basis.