Pre-implantation genetic diagnosis of embryos - PGD

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Several decades ago the medical science had no means to estimate the condition of health of a baby still to be born. Parents who were carriers of genetic diseases treated the birth of a healthy baby as a miracle.

On our day and age, the rapid development of attendant reproductive methods and, in particular, pre-implantation genetic diagnosis of embryos (PGD), which is applied in IVF programs, enabled medics to predict, with a high degree of precision, if your baby will be born healthy.

Pre-implantation genetic diagnosis of embryos (PGD) represents special molecular-biological testing of chromosome sets of oocytes or embryo cells, which is conducted prior to transfer an embryo into the uterine cavity. Such a research enables to identify some 150 genetic diseases. PGD permitted to materially enhance the effectiveness of infertility treatment, using the IVF method. In this case, the risk of birth of an unhealthy child is considerably reduced.

PGD – medical indications

This procedure is applied to family couples who face the following problems:

  • age category exceeds 35 years;
  • chromosome and genetic pathologies were detected in sex cells;
  • spermatogenesis dysfunctions;
  • at least two failed IVF attempts;
  • customary failure to carry pregnancy full term (two or more miscarriages);
  • death of children at time of previous pregnancies as result of rhesus-conflict; 

The PGD technique permits to identify the following diseases of a child to be born;

  • Gaucher’s diseases;
  • Fanconi’s anemia;
  • Huntington’s disease;
  • torsion dystonia;
  • neurofibromatosis;
  • polycystic renal disease;
  • Down’s, Edwards’, Alport’s, X-fragile chromosome syndromes;
  • mucoviscidosis;
  • haemophilia;
  • phenylketonuria;
  • pigmented retinitis;
  • myodystrophy;
  • retinoblastoma;
  • pemphigus;
  • myopathy;
  • achondroplasia;
  • many other genetic diseases

Pre-implantationgeneticdiagnosis – procedure

The PGD process may only be applied as part of the IVF/ICSI cycle, which is due to the fact that at the stage of standard IVF a large quantity of male sex cells is added to an egg, and at the time of collection of the matter both embryo cells and parts of spermatozoa not involved in fertilization may be subject to analysis.

To carry out the diagnostics, the following methods can be used:

  1. FISH method applied in the event of numeric and structural chromosome dysfunctions, to avoid miscarriages and enhance likeliness of pregnancy;
  2. PCR (polymerase chain reaction) method applied to identify monogenic diseases, if at least one parent is their carrier, or suffer such diseases

To qualify for the PGD procedure, spouses must be tested for genetic defects. In cases of identified mutations or unclear nature of inheritance of genetic problems, pre-implantation diagnosis may not be possible.

Under PGD conditions, cell biopsy can be applied at the following stages:

  • polar body biopsy at stage of oocyte/zygote;
  • biopsy at stage of fragmentation; 6-10-cell embryo;
  • embryo cell biopsy at stage of blastocyst

Under condition of polar body biopsy, only mother chromosomes are analyzed. This method is used in those cases where the gene factor is inherited in female line. Such an analysis enables to assess the condition of health of an egg, without causing any damage to it. If an oocyte does not have any defects, it is fertilized and transferred into the uterus.

Biopsy conducted at the stage of fragmentation involves the analysis of 1-2 separated blastomere cells. While the diagnosis is carried out, the embryos continue to develop, and on day five the best of them are transferred into the uterine cavity.

The analysis of embryos at the stage of blastocyst is repeated only in those cases where the results produced at the stage of fragmentation give rise to doubt.

In most cases the polar bodies are first analyzed, which is followed by the blastomere analyses, thus, enhancing the precision of diagnostics.