Preimplantation genetic diagnosis

What is preimplantation genetic diagnosis?

Preimplantation genetic diagnosis is a technique that enables the detection of chromosomal abnormalities and hereditary diseases in embryos obtained by in vitro fertilisation (FIV). PGD enables high genetic risk couples to have healthy children thanks to the genetic selection of embryos.

What is the legal framework?

Preimplantation Genetic Diagnosis falls within article 12 of Law 14/2006 dated 26 May, on assisted human reproductive technology.

When is PGD currently recommended?

  • Chromosomal abnormalities. The aim is to reduce the risk of generating chromosomally unbalanced embryos in parents who are carriers of reciprocal translocations, Robertsonian translocations or inversions.
  • Monogenic diseases. Embryos that are free from diseases such as cystic fibrosis, Huntingdon’s disease, fragile X syndrome or haemophilia, among others can be selected. Less prevalent monogenic diseases which are the product of known mutations can also be diagnosed.
  • Screening for aneuploidies. In these cases we recommend a full study of all of the embryo’s chromosomes. Couples who have experienced repeated miscarriages, and women of advanced maternal age can benefit, and it can also be helpful where there have been repeated unsuccessful, attempts at implantation.
Can embryos be selected for other purposes?

Currently it is possible to use PGD for other purposes with the express permission of the National Commission for Assisted Human Reproduction (CNRHA).

What exactly is PGD?

It is an embryo biopsy (the extraction of one or more cells) carried out when the embryo is at the 6 to 8 cell stage (3 days after follicular puncture) or on embryos at the blastocyst stage of development (day 5) by means of the extraction of trophectoderm cells.

For example, for screening the following techniques can be applied:

  • NGS (Next Generation Sequencing). This technique is used for the full study of all 24 chromosomes (checking for both numerical and structural abnormalities)
  • PCR (Polymerase chain reaction) for the study of genetic mutations that cause monogenetic diseases

Once the diagnosis is complete, the transfer of those embryos that are not the carriers of chromosomal alterations or hereditary genetic diseases will take place.

How reliable is the technique?

It is more than 90% reliable. Even so, prenatal screening during pregnancy is recommended, in order to minimise the possibility that the screening produced a false negative.

Are there any associated risks or side effects?

No, in terms of side effects during the IVF cycle, there are no differences between patients who have had a PGD, and those who have not.
With regard to the biopsy procedure, the likelihood of any damage to the embryo is very low, no higher than 0.6%, according to data collected by Hospital Clínic.

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