Genetic Testing

What is Preimplantation
Genetic Testing (PGT)?

PGT is a test that analyzes the DNA of oocytes (polar bodies) or embryos (blastocysts) for HLA typing or identification of genetic abnormalities.
In other words, this is a method that allows to test an embryo before using it in ART programs. For this, those cells are used that go beyond the embryo membrane (usually on the 5-6th day of their development), from which the chorion, and subsequently the placenta, is formed. The embryo is not damaged during this procedure. PGT increases the chances of a successful pregnancy.

  • PGT-A - for the determination of aneuploidies;
  • PGT-M - for monogenic diseases;
  • PGT-SR- diagnostics of embryos in carriers of chromosomal rearrangements (inversions, translocations, deletions).

Preimplantation genetic diagnostics (PGD)

Preimplantation genetic diagnostics of embryos is aimed at identifying the transmission of genetic pathology by inheritance. It can be recommended if the spouses are blood relatives and if one or both future parents have:

  • reciprocal translocation;
  • sex chromosomes abnormalities;
  • Robertsonian translocation;
  • monogenic diseases.

Therefore, it is necessary to consult a geneticist and select an individual method of preimplantation genetic testing.

Methods of embryo testing:

  • FISH

    This method lies in the fact that special DNA probes, selected for each chromosome, are placed in the nucleus of the embryonic cell and coloured with various fluorescent (luminous) stains. Hybridization of the DNA probe with the corresponding chromosome occurs. With the help of a luminescence microscope or special programs, it is possible to obtain an image of the nucleus with fluorescent stains, which allows to determine commonly occurring chromosomal abnormalities. The screening panel includes 5 chromosomes: sex-X, Y, as well as 13, 18, and 21.
    To use this method, a biopsy of embryonic cells is performed on the 4th day of development. The duration of the procedure is 12-48 hours. By the 5-6th day of embryo development, the result of this genetic screening is already known.

  • Comparative genomic hybridization (array-CGH)
  • NGS (Next Generation Sequencing)

    This is the latest molecular genetic technology using DNA microarrays. With the help of this method, it is possible to determine not only the number but also in some cases structural abnormalities of all 24 chromosomes.
    For diagnostics, a biopsy of trophectoderm cells is performed, and the embryos themselves must be cryopreserved (frozen).

Indications for PGT-A (preimplantation Genetic Testing for Aneuploidies)

  • mother's age (38+);
  • the repeated absence of implantation in ART cycles;
  • habitual miscarriage;
  • severe male infertility;
  • couples with normal karyotype and multiple pregnancy losses.

Preimplantation Genetic Testing for Monogenic disorders (PGT-M)

PGT-M is used to test for certain genetic pathogenic variants (mutations) associated with known diagnoses or family heredities (i.e., it is a monogenic disease (mutation) in a particular gene).
It is recommended to consider the use of PGT-M for pre-transfer embryo diagnostics if:

  1. a woman or a man in a couple is a carrier of an autosomal recessive condition (for example, a carrier of cystic fibrosis, phenylketonuria, etc.);
  2. there are conditions associated with an autosomal dominant type of inheritance (for example, Huntington's disease);
  3. a woman is a carrier of a disease linked to the X chromosome (for example, haemophilia);
  4. there was a pregnancy or a child with a monogenic disease.


It is a change in the size or structure of chromosomes that contain genetic material.
It is carried out if a chromosomal rearrangement has been diagnosed in previous pregnancies, or when a structural rearrangement in the chromosomal apparatus of parents has been established:

  • inversion – chromosomal rearrangement, in which there is a rotation of the chromosome region by 180 degrees;
  • mutual translocation – when two regions from two different chromosomes break and change places, or when one chromosome joins the other.

It is important to remember that:

  • people with balanced translocations are generally healthy. But problems can arise at the stage of childbirth;
  • translocations can arise spontaneously and be inherited from parents;
  • translocations cannot be corrected or cured – they remain for life.

Also, it’s worth keeping in mind that:

  • regardless of the type of preimplantation genetic testing, false-positive and false-negative results are possible;
  • patients / healthcare professionals should be informed that a “normal” or “negative” PGT result does not guarantee birth of the baby without genetic pathology;
  • traditional diagnostic tests or screening for aneuploidy should be offered to all pregnant women after PGT-A;
  • this is especially important after PGT-M and PG-SR if no PGT-A has been performed;
  • testing is not carried out for all monogenic diseases at the same time and does not reveal pathogenic variants de novo.

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