Preimplantation Genetic Diagnosis (PGD) & Preimplantation Genetic Screening (PGS)

Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are diagnostic methods allowing to determine the presence or absence of genetic dispositions for certain diseases in the genetic profile of embryos prior to their implantation.

• The purpose of PGD is to prevent genetic diseases in families with a history of heritable diseases.
• The main purpose of PGS is to increase the chance of pregnancy and to prevent spontaneous miscarriage.

Procedure:

- On the 3rd day after fertilisation, 1 to 2 blastomeres are extruded, typically from an embryo in the eight-cell stage;
- On the 5th or 6th day of the expanded blastocyst development stage, several trophoectoderm cells are collected.

Genetic Analysis Methods

– Fluorescence in situ hybridisation (FISH) is a method allowing to examine the most common chromosomal numerical abnormalities (e.g. trisomy 21 – Down syndrome, trisomy 18 – Edwards syndrome, or trisomy 13 – Patau syndrome), as well as certain structural aberrations in chromosomes (translocations);

– Array comparative genomic hybridisation (Array CGH) is a molecular cytogenetic method allowing to analyse the entire karyotype using blastomeres or trophoectoderm cells;
– Polymerase chain reaction (PCR) is a method used to diagnose monogenic disorders.

PGD/PGS are recommended to couples in the following cases:

• PGD

– If there is a risk of the transfer of a congenital chromosomal aberration that jeopardises the pregnancy by spontaneous miscarriage, birth defects or stillbirth (couples where genetic tests have ascertained numerical or structural abnormalities in their chromosomes);
– If there is a risk of the passing of a serious inherited monogenic disorder;
– If there is a history of recurring miscarriages or births of a fetus with a chromosomal disorder;
– If there is a family history of sex-linked diseases;
– If there are other genetic risks indicated by a medical geneticist.

• PGS

– If there is a history of repeated failures of assisted reproduction methods;
– If the age of the mother is over 35 years;
– If the partner suffers from a more severe disorder in spermatogenesis (oligoasthenoteratospermia);
– If there is a history of recurring miscarriages in the early stage of pregnancy.