PGT-SR – genetic testing of embryos for structural abnormalities

For some couples, difficulties in achieving or maintaining a pregnancy may be due to structural chromosomal changes in one of the partners. PGT-SR is a genetic test on embryos carried out during in vitro fertilisation treatment at Invimed, which helps to select the embryos with the greatest developmental potential. This makes it possible to reduce the risk associated with chromosomal abnormalities and support patients on their journey towards a healthy pregnancy.

What is PGT-SR testing?

PGT-SR is a pre-implantation genetic test of embryos carried out during in vitro fertilisation. It is intended for patients who are carriers of balanced structural chromosomal changes, such as translocations and inversions. Although individuals who are carriers of such changes often have no apparent health symptoms, they may experience fertility problems, such as unexplained male infertility (e.g. low sperm count), implantation failures or recurrent miscarriages. PGT-SR enables the identification of embryos with a normal chromosome structure and the selection of those most likely to develop normally

What are structural chromosome aberrations — translocations and inversions?

Let’s imagine that our genome is like a library. Chromosomes are the shelves holding the books, and genes are the information written on their pages. Each book has its own specific place, which ensures that the whole library is well-organised and runs smoothly.

Chromosomal aberrations These are situations in which changes occur within this ordered system. If the number of shelves is greater or fewer than it should be, we refer to these as numerical aberrations. If the number of shelves remains the same but the arrangement of the information on them changes, we are dealing with structural aberrations. This group includes, amongst others, translocations and inversions.

Translocation This is a situation in which a book or part of a book is moved from one shelf to another. The amount of information remains the same; only its location changes.

Inversion It is like a situation where a section of a book is taken out, rotated by 180 degrees and placed back in the same spot. The information is still on the same shelf, but its orientation is reversed.

Although individuals who are carriers of a translocation or inversion often have no health symptoms, these abnormalities can affect the reproductive process. Therefore, for patients who are carriers of such changes, pre-implantation genetic testing for chromosomal abnormalities (PGT-SR) can be carried out to help identify embryos with a normal genetic makeup.

How does PGT-SR differ from PGT-A?

Both PGT-A and PGT-SR are genetic tests carried out on embryos during in vitro fertilisation. In both cases, the embryologist removes a few trophectoderm cells via biopsy and then sends the sample for genetic analysis.

However, each test has a slightly different purpose. PGT-A checks whether the embryo has the correct number of chromosomes. PGT-SR is carried out on patients who are carriers of a translocation or inversion; in addition to assessing the number of chromosomes, it also analyses abnormalities resulting from changes in their structure.

A karyotype analysis revealed an abnormality in the structure of the chromosomes in one of the partners,
the couple had suffered recurrent miscarriages,
previous embryo transfers had been unsuccessful,
There has been a case in the family of a condition linked to changes in chromosome structure.

How is the examination carried out?

An embryo biopsy is usually carried out on day 5 of development, at the blastocyst stage. If, by day 5, the blastocyst is not sufficiently developed – particularly with regard to the trophectoderm cells – embryo biopsy may be carried out on day 6 or 7. An experienced embryologist collects several trophectoderm cells from the embryo. The collected material is then preserved and sent for genetic analysis. Embryos that have undergone PGT-SR testing are vitrified (frozen).

In the genetics laboratory, genetic material (DNA) is isolated from the embryo cells that have been collected and analysed using an NGS sequencer.

Once the results of the genetic test have been received, the doctor and the embryologist decide which of the genetically normal embryos are suitable for transfer. In appropriate cases, a genetic consultation is recommended.

IMPORTANT: Before commencing the procedure involving PGT-SR testing, the couple must provide the attending doctor with the karyotype results of the person who is a carrier of the structural chromosomal abnormality. This will enable the genetic analysis to be tailored to the couple’s individual situation, or, if necessary, for additional tests to be commissioned in order to improve the accuracy of the results obtained.

How long does it take to get the result?

The results of a PGT-SR test are usually available within 2–3 weeks. In some cases, the waiting time may be slightly longer. It is advisable to confirm this timeframe with your doctor or embryologist.

Glossary of terms

Translocations

Translocations – the transfer of genetic material between two different chromosomes.

Inversions

Inversions – the inversion of a chromosome segment within the same chromosome.

The medical information presented should be considered as general guidelines and does not replace the individual judgement of the doctor regarding the medical management of each patient. The doctor, after a thorough examination of the patient's condition, determines the extent and frequency of diagnostic tests and/or therapeutic procedures, taking into account specific medical indications. All medical decisions are made in full consultation with the patient.

Author of the article

Invimed editorial team - we serve patients by solving their fertility problems. We use world medical knowledge, state-of-the-art technology and treatment methods. We are here to make dreams of parenthood come true. The smiles on the faces of happy parents give meaning to our work.

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