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preimplantation genetic diagnosis

DEFINITION:

It is an assisted reproduction technique complementary to In Vitro Fertilization that allows the detection of genetic abnormalities in an embryo before being transferred to the woman's uterus, thus maximizing the possibility of having healthy offspring.

INDICATIONS:

  • Risk of transmitting chromosomal alterations or monogenic diseases.
  • Implantation failures after several embryo transfers.
  • History of repeat abortions.
  • Altered male factor: detection of meiosis alterations in sperm.
  • Advanced maternal age: recommended from 38/39 years of oocyte age.

PROCESS

In order to analyze an embryo, it is necessary, first, to biopsy it. On the 5th day of embryonic development, when the embryo is in the Blastocyst state by means of laser technique, a fragment of the trophectoderm is extracted without this compromising its correct embryonic development. The genetic analysis is carried out on several cells allowing to select those embryos with a diagnosis of normality. With this technique, we can detect a higher percentage of Mosaic embryos in which several cell lines (normal and altered) coexist.

Microarray Comparative Genome Hybridization test of 24 chromosomes (aCGH-24)

Technique that allows assessing numerical and / or structural chromosomal abnormalities of the biopsy performed. Comparative Genomic Hybridization (aCGH) arrays allow analysis of multiple regions across each and every chromosome. First, a total amplification of the genome (WGA) is carried out and then the DNA is fluorescently labeled and hybridized on BAC arrays.

TWO PROCEDURE POSSIBILITIES:

DGP -FRESCO: The embryos are biopsied on day 5 of embryonic life. The result is obtained in 24 hours and the euploid embryos (genetically normal) are transferred in the same cycle. The remaining euploid embryos will be frozen for later transfers.

DGP- DEFERRED: A biopsy is performed on the embryos that arrive in the Blasto state and are frozen without knowing the results. Three weeks later we will have the result. Normal embryos will be kept frozen to be able to transfer at the right time.

INDICATIONS:

  • NON-RECEPTIVE ENDOMETRIUM (active bleeding, elevated estradiol levels)
  • NEED TO ACCUMULATE EMBRYOS (the more embryos biopsied, the greater the probability of having normal embryos; depending on the antecedent of the couple)

What does the Spanish legislation say about PGD?

According to laws 35/1988 and 14/2006 on Assisted Reproduction Techniques, any intervention on the embryo for diagnostic purposes will have no other purpose to treat a disease or prevent its transmission, with reasonable and proven guarantees, and this under the following requirements:

Non-pathological hereditary characters are not influenced, nor is the selection of individuals or race sought.

It must be carried out in authorized health centers and by qualified teams equipped with the necessary means.

The couple, or where appropriate, the single woman, has been duly informed about the procedures, diagnostic tests, possibilities and risks of the proposed therapy and has previously accepted them.

That diseases are treated with a very precise diagnosis, with a serious or very serious prognosis, and when they offer guarantees, at least reasonable, of the improvement or solution of the problem.

What else should we know?

There is a variable percentage of the embryos analyzed in which it is not possible to obtain any conclusive results, and that the team recommends not to transfer. This occurs in <3% with Array Technique on Blasto.

The embryo biopsy does not affect the development of the fetus, because the embryonic cells maintain their full potential.

The biopsy in Blasto has a greater capacity for success compared to Day 3. First, there is a natural selection of the embryos, since they are left in culture for five days and many of them are blocked before reaching Blasto. Therefore, there is a smaller number of biopsied embryos, but a greater implantation potential of normal embryos compared to biopsies at day +3.

It may happen that the cells analyzed do not present alterations, but that other cells of the same embryo do have genetic abnormalities, this phenomenon is known as mosaicism and limits the effectiveness of the technique. The probability of Undetected Mosaicism is <5%.

It is recommended that the mother undergo a classic prenatal diagnosis (amniocentesis, chorion biopsy) to confirm the diagnosis, since there is a certain error rate in the PGD technique (<5%).

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