Preimplantation Genetic Screening – PGS

Preimplantation Genetic Screening (PGS) is a method for testing the chromosomes of embryos that result from IVF, using special diagnostic techniques for genetic analysis.

The purpose of the test is to ensure the transfer of healthy embryos to the woman’s uterus, in order to increase the success rate for that IVF cycle and the birth of healthy babies.

When it is recommended

Preimplantation Genetic Screening is recommended in the following cases:

  • Women over the age of 36 undergoing IVF
  • Couples with a history of multiple miscarriages of unknown cause in the first trimester of pregnancy
  • Couples with a history of multiple failed IVF attempts
  • Couples with a family history of chromosomal anomalies

How it is implemented

The process of preimplantation genetic screening involves a biopsy of the embryo during the 3rd or 5th day of development for embryos derived through IVF. There follows an examination of all the chromosomes in the biopsy sample using highly precise and sensitive molecular biology techniques, such as microarray-based Comparative Genetic Hybridisation (microarray CGH) and Next Generation Sequencing (NGS). The microarray CGH technique permits the tracing of aneuploidies in all 24 chromosomes, as well as unbalanced derivatives of chromosomal rearrangement agents, while NGS is based on complete genome scanning to examine multiple sites.

When the biopsy occurs on the 3rd day, embryos are cultured until the 5th day of development and, based on the outcome of the preimplantation genetic screening, normal embryos are transferred or cryopreserved. When the biopsy occurs on the 5th day, the embryos are frozen immediately after the biopsy procedure and normal embryos are used in a subsequent IVF cycle.

Advantages of preimplantation genetic screening

The transfer of embryos with a normal number of chromosomes increases the rate of implantation and reduces the frequency of first-trimester miscarriages by 15%. At the same time, preimplantation genetic screening reduces the chances of children being born with chromosomal anomalies, such as trisomy 21, also known as Down syndrome.