Preimplantation genetic diagnosis (PGD) is a reproductive technology used during an IVF cycle. PGD can be used for diagnosis of a genetic disease in early embryos before implantation or pregnancy. Each cell in our body has 46 chromosomes (23 from the father and 23 from the mother). The chromosomes are made up of a substance called DNA that contains our genetic information. Information is distributed in the genes and there are two copies of each gene, one originating from the mother and the other from the father.

Alterations in the chromosomes that cause diseases

• Numerical alteration: This is an irregularity that affects the number of copies of a chromosome. The most well known example is the Down’s Syndrome, in which there are three copies of chromosome 21 instead of two.
• Structural alteration: This is an irregularity in the structure of a chromosome.
• Monogenic diseases: These are genetic diseases caused by a fault or mutation in a single gene. Examples of these diseases are Cystic Fibrosis, Haemophilia, X Fragile Syndrome, Myotonic Dystrophy, and Huntington’s Disease among others.

Diagnostic methods

During pregnancy, there are two types of diagnosis to establish chromosomal and genetic alterations in the foetus:

• Pre-natal diagnosis (PND): Amniocentesis is the most common PND method.
• Preimplantational Genetic Diagnosis (PGD): PGD is an early prenatal diagnosis made on the embryo on its third day of development before being transferred to the uterus. PGD enables embryos that are free of the disease being studied to be transferred to the mother.

PGD is recommended for

• Couples at risk of transmitting chromosomal alterations or monogenic diseases.
• Couples with a clinical history of repeated abortions or miscarriages.
• Implantation failure after several attempts with IVF.
• Alterations in the meiosis of the spermatozoa.
• Women of advanced age.