PGD (PREIMPLANTATION GENETIC DIAGNOSIS)

PGD method involves specialized high-precision and technology intensive examination of embryo cells for identification of possible abnormalities and genetic disorders prior to embryo’s transfer into the uterine cavity. Therefore, with the help of PGD only healthy embryos are selected for transfer.

For patients with inherited genetic abnormalities this is an alternative way to reduce the risk of pregnancy with an ill fetus and birth of a child with genetic diseases.

pgd_diagnostics

Indications for preimplantation diagnosis:

  • age of spouses over 35 years old;
  • previous unsuccessful attempts of IVF, spontaneous abortions;
  • history of missed abortion, especially at early stages;
  • determination of child’s sex – in case of carriage of X-linked genetic diseases;
  • detection of chromosomal abnormalities during karyotyping spouses;
  • severe spermatogenesis impairment, occasional sperm cells nad high percent of abnormal sperm cells.

 

Preimplantation diagnosis is carried out after obtaining of follicles and fertilization, during the period of embryo development in vitro (in a tube) and before transfer into the uterine cavity. Genetic material of an embryo is used as a material for genetic testing during PGD. On the third day, an embryo consists of 6-8 cells called blastomeres. One blastomere is removed for genetic analysis; the method is called “embryo biopsy”. It should be noted that this procedure does not affect further embryo development.

While genetic diagnosis is being performed, embryos continue to develop in an appropriate medium until transfer into the uterine cavity at day 5 of development. By this time, an embryo has reached the state of a blastocyst. Before transfer an embryologist assesses structure and shape of embryos (morphology).pgd_diagnostics_in_ukraine The result of genetic diagnosis is related to embryos structure and conclusion is made regarding which embryos are recommended for transfer into the uterus. The best embryos, in terms of their morphological characteristics and absence of genetic disorders, are selected for transfer.

Genetic tests performed as part of PGD are technology intensive. Analysis is carried out in very short terms on the basis of a very small amount of material, i.e. polar bodies and blastomeres collected by biopsy. The final stage is a transfer of one or more selected healthy embryos into the uterine cavity.

 

Many future parents are concerned whether PGD procedure may harm child’s health. Blastomere’s collection is performed at day 3 when cells of an unborn child are still universal, undifferentiated and some cells can be replaced by other cells without any harm to health. Collection of polar bodies is considered even less invasive for an embryo. Risks of using PGD are primarily associated with general risks of the IVF program (e.g., the risk of ovarian hyperstimulation syndrome).

 

PGD increases chances of pregnancy onset as the result of IVF since healthy and viable embryos are selected for transfer into the uterine cavity. In case of pregnancy onset probability of genetic disorders of an unborn child will be minimal.

 

On the other hand, regrettably for a married couple, PGD results may indicate presence of genetic abnormalities in each of the embryos obtained. In this case, this couple should undergo the whole procedure from the very beginning (including karyotyping). Transfer of embryos into the uterus will not be performed until at least one healthy embryo is identified with PGD

 

NGS method in preimplantation genetic diagnosis

NEXT GENERATION SEQUENCING (or NGS) is a method of direct analysis of embryo genome.

 

Advantages of the method.

  • Possibility to examine all 24 chromosomes simultaneously with previously unattainable precision at the level of 99.999% which is the most precise result for now.
  • Reliable result. During NGS testing each sample is assigned with special molecular code which eliminates the possibility of errors, beginning with the stage of material collection from an embryo.
  • Safety of an embryo: reduction of the number of biopsies required for diagnosis. One embryo biopsy is enough to obtain a reliable result.
  • NGS method has been recognized as a reference for all other techniques, primarily, due to a direct way for decoding of genetic material.

With the help of the methods used previously material was examined in an indirect way. Therefore, nowadays, there is a growing tendency of turning to NGS technology for preimplantation diagnosis.

  • Possibility to combine examination of chromosomes and testing for monogenic disorders in a single analysis procedure! Until now, it has not been possible to combine testing for chromosome aneuploidies and monogenic disorders. Today this is possible with the help of NGS and one biopsy of an embryo is just enough.
  • The problem of mosaicism among embryos (presence of cells with a different chromosome set in an embryo) remains unresolved so far.

None of the previously used methods were able to accurately show whether a given embryo has mosaicism. If there is a limited number of embryos for transfer, knowledge of relationship between clones is crucial. NGS most clearly indicates presence of mosaicism allowing for selection of genetically healthy embryos for transfer.

 

For the moment, only cost can be considered as a disadvantage of this method.

 

 

Difference between PGD methods

 

PGD method Possible amount of chromosomes examined Method accuracy Characteristics Detection of mosaicism in an embryo
FISH 6 airs of chromosomes 97% It is not possible to diagnose minor structural changes in chromosomes It is not possible to exclude an event of mosaicism
Array CGH 23 airs of chromosomes 97% It is not possible to diagnose quantitative chromosomal abnormalities divisible by the haploid set The risk of mosaicism remains
NGS all 24 airs of chromosomes 99.999% Possibility of studies in the area of various monogenic diseases of known genetic etiology Possibility to diagnose mosaicism

 

Far from all clinics have mastered this innovative method of NGS.

Our partners have already been successfully employing it in their work and provide our patients with additional chances in the form of the best IVF results.

 

 



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