PGT-A – genetic testing of embryos for aneuploidy 

At Invimed, pre-implantation genetic testing to detect aneuploidy in embryos is carried out using the advanced technique of Next-Generation Sequencing (NGS). This technique enables a detailed analysis of the entire embryo genome to detect numerical chromosomal abnormalities (aneuploidy). 

What is PGT-A testing? 

PGT-A is a genetic test carried out on embryos prior to transfer during in vitro fertilisation. It enables an assessment of whether an embryo has the correct number of chromosomes (euploidy). This is crucial information during infertility treatment, as aneuploidy – an abnormal number of chromosomes – can lead to implantation failure, miscarriages and genetic disorders such as Down’s syndrome, Edwards’ syndrome, Patau’s syndrome or Turner’s syndrome.  

What does the PGT-A test detect?

PGT-A testing detects numerical chromosomal abnormalities. 

Any abnormalities in chromosome number can cause foetal malformations and lead to genetic disorders, such as Down’s syndrome (an excess of genetic material in the form of an extra, third chromosome 21 or part thereof, known as trisomy 21, or Patau’s syndrome (trisomy 13). 

PGT-A detects genetic disorders caused by aneuploidy (an abnormal karyotype in terms of chromosome number), such as: 

• Down's syndrome, 

• Edwards syndrome, 

• Patau syndrome, 

• Klinefelter syndrome, 

• Jacobs syndrome, 

• band XXX, 

• Turner syndrome, 

• Warkany’s band 2. 

You can find out more about disorders associated with an abnormal karyotype on the following page:Karyotype. 

What is the difference between PGT-A and PGT-A+? 

Both tests share the same objective: to detect abnormalities in chromosome number, i.e. aneuploidy in embryos. However, the PGT-A+ test offers a more comprehensive genetic analysis than conventional PGT-A. It combines aneuploidy analysis using next-generation sequencing (NGS) with the assessment of single-nucleotide polymorphisms (SNPs), providing more comprehensive information.  

In the PGT-A+ test carried out at Invimed: 

• Two methods are used – NGS and SNP – which means that the analysis not only allows for the identification of aneuploidy and the assessment of mosaicism in embryos, but also enables the reliable detection of all ploidy abnormalities, such as haploidy and triploidy.  

• We minimise the risk of errors through enhanced checks on sample compliance and the detection of DNA contamination from other sources, such as the mother. 

• Through what is known as a ‘cohort check’, we verify the genetic compatibility between embryos, confirming their kinship and reinforcing the quality control of the test carried out. 

• We use the MitoScore mitochondrial biomarker, which assesses the embryo’s energy potential and helps to select the one with the highest implantation potential, thereby increasing the chances of a successful in vitro treatment.  

Assessment of aneuploidy  

The test identifies embryos with a normal number of chromosomes and detects monosomies, trisomies and other chromosomal abnormalities.  

Assessment of ploidy 

The test makes it possible to distinguish between diploidy (a normal set of 46 chromosomes), haploidy (a single set of chromosomes) and triploidy (the presence of three sets of chromosomes). Triploidy is a significant cause of spontaneous miscarriages and may not be detected in a standard PGT-A test.  

Assessment of pollution 

SNP analysis makes it possible to detect the presence of foreign DNA in trophectoderm biopsy samples. This makes it possible to identify cases of contamination with cells of maternal origin or those arising during laboratory procedures, and to rule out results that may be prone to misinterpretation.  

Cohort check 

It is possible to confirm the genetic compatibility of embryos belonging to the same patient couple. This provides an additional element of quality control and verification of the origin of the genetic material.  

How does the PGT-A test work? 

NGS sequencing, which is used for PGT-A genetic testing, is a state-of-the-art technique that allows rapid analysis of the entire genome of an embryo, thanks to so-called parallel sequencing, which is the reading of the nucleotide sequence of a DNA molecule.

When should a PGT-A test be carried out?

It is advisable to undergo PGT-A and PGT-A+ testing when: 

• the patient is over 35 years of age, 

• there are recurrent miscarriages or implantation failures,

• the couple have a child with a genetic condition (e.g. Down’s syndrome),

• an abnormal karyotype has been detected in one or both partners,

• the patient has significantly reduced semen analysis results, in particular an abnormal SCD (sperm DNA fragmentation) result,

• Other indications emerged during the medical interview.

Where do we carry out PGT-A testing?

The PGT-A test is carried out at every Invimed centre. Invimed works in partnership with Europe’s largest genetic laboratory – Igenomix. A team of world-renowned scientists has been leading Igenomix for over a dozen years. Igenomix possesses the largest gene libraries, as well as top-of-the-range NGS sequencers. 

Frequently asked questions

Bibliography

1. Good practice recommendations from the European Society of Human Reproduction and Embryology for pre-implantation genetic testing (PGT)
2. R. Kurzawa, R. Spaczyński, „Diagnosis and treatment of infertility. Standards of the Polish Society for Reproductive Medicine and Embryology and the Polish Society of Gynaecologists and Obstetricians.”