PGD

What is it?
Preimplantation Genetic Diagnosis (PGD) consists of the study of the genetic and chromosomal constitution of an embryo before it is transferred into the uterus. The aim of this study is to detect embryos with specific genetic or chromosomal abnormalities. It is carried out in those cases where medical advice so requires it.

When is it advised?
This study is recommended:

1. For couples with irregular karyotypes.
2. For men with chromosomal alterations in germinal cells The diagnosis of these abnormalities is done through a FISH study of sperm and/or a meiotic study of testicular biopsy.
3. For women older than 37 The PGD technique in these three instances is FISH, a chromosomal study.
4. For patients with genetic illnesses (not chromosomal) that can be passed on, to avoid having affected children. In these cases, the PCR technique is applied.
5. It is necessary to know the problem in each case in order to inform the patients and recommend the most appropriate Preimplantation Genetic Diagnosis (PGD) technique.

How is it done?
The technique used includes a biopsy (taking a sample) of each embryo when it consists of 6 to 8 cells, normally 3 days after egg extraction and ICSI.
The embryo is extracted through a hole made in its protective layer (zona pellucida). It is considered that the cell from the biopsy, specifically its nucleus, is a reliable sample of the genetic and chromosomal constitution of each embryo.

A study of the nucleus of the extracted cell is done, either by FISH (fluorescent in situ hybridisation of DNA) or PCR (amplification of a segment of DNA through polymerase enzyme action). This study takes one day and the transfer of normal embryos is carried out on day four, in other words, one day after the normal time period.

Limits of Preimplantation Genetic Diagnosis (PGD)
It must be stated that this is a partial study of genetic material, therefore it cannot provide information on all possible chromosomal or genetic abnormalities present in the embryo. It only provides information on what was studied in each case.