Couples who undergo an IVF cycle may ask to be informed on the state of health of the embryos (Article 14, paragraph 5, Law 40/2004). In these cases, if there is an indication, we can proceed with the pre-implantation genetic diagnosis.
The pre-implantation genetic diagnosis (PGD) is a procedure to identify the presence of inherited genetic disorders or chromosomal abnormalities in embryos in the very early stages of development.
Indications for pre-implantation genetic diagnosis are:
The genetic test can be performed on the oocyte polar body, on a single embryonic cell taken on the third day of culture in vitro (blastomere) or on several cells from the trophectoderm layer, extracted on fifth and/or sixth day of development. The sampling technique implies to drill a hole in the zona pellucida surrounding the embryo using a laser beam. The cells are placed in test tubes, through the use of a micromanipulator ,and sent to the molecular genetics center that will carry out the analysis (see figure).
PGD uses two molecular techniques:
Preimplantation genetic screening is a procedure to identify the presence of chromosomal abnormalities in embryos in the very early stages of development.
The embryonic chromosomal study (abnormalities in chromosome number) is indicated for patients with advanced age, patients with chromosomal mosaicism and patients with repeated implantation failures or recurrent pregnancy loss.
PGS is performed by qPCR (quantitative polymerase chain reaction).
The qPCR technique is a molecular biology technique to analyze numerical abnormalities of the totality of chromosomes of our genome. The entire structure of the embryo chromosomes is analyzed using the technique based on real time PCR and analysis of the number of copies of each chromosome (Treff et al., Fertil Steril 2012). This procedure allows the identification of numerical chromosomal abnormalities (aneuploidy) of the 22 autosomes (chromosomes from no. 1 to no. 22) and the sex chromosomes (X and Y).