Latest update: 10/05/2017


In PGS or pre-implantation genetic screening we count the number of all chromosome pairs in one or several cells of the embryo. Embryos with an abnormal number of chromosomes are termed aneuploid, hence this technique is also called ‘screening for aneuploidy’. Aneuploid embryos are not returned to the uterus because they are not viable or can give rise to the birth of a child with problems.

Difference between PGD and PGS

  • In PGD we are looking for one particular hereditary gene defect: in the lab we already know what defect on what chromosome or gene we are looking for.
  • In PGS by contrast we are not evaluating one particular gene or chromosome, rather we count the chromosomes in the cells that we have obtained from the embryo.
    Thanks to PGS we can make a selection in the lab of fertilised embryos, not only based on their morphology (the structure and the number of cells), but also on their chromosomal contents.


The value of PGS

Today there is much discussion about the value of PGS. A number of studies have demonstrated that it does not increase the chance of pregnancy. In a number of cases PGS can however help us to understand IVF failure better.
The new techniques of genetic screening using microarrays are nevertheless promising. They are more accurate and enable all chromosomes to be analysed.
Whatever the verdict, further studies are necessary to confirm the added value of aneuploidy screening in the context of IVF treatment.

If your doctor prescribes PGS because it may be useful to you, the PGD clinic will try to genetically screen as many embryos as possible. Depending on the number, the quality and the genetic condition of your embryos it is however always a possibility that no embryos can be transferred.