Lister Hospital, London

Analysis of the Impact of Human Embryo Mosaicism on the Reliability of Pre-implantation Genetics Screening (PGS) (R0163)

Licence holder: Dr Debbie Taylor

Lay summary:

Certain IVF patient groups have been identified as being more at risk of producing embryos with chromosomal abnormalities. These chromosomal abnormalities usually cause failure of implantation following repeated IVF embryo transfers, or miscarriages. In a minority of cases the embryos can develop to cause a pregnancy affected by a chromosomal abnormality such as trisomy 21 also know as Down's syndrome.

Preimplantation genetic screening (PGS) is a technique, which allows embryos produced during an IVF treatment cycle to be tested for specific chromosomal abnormalities. Following the screening procedure only embryos that are identified as being normal for the chromosomes being analysed are considered for embryo transfer. Due to the increased selective powers provided by this procedure, PGS has been shown to improve both implantation rates and live birth rates in specific patient groups. The screening process involves looking at the chromosomes present in a single cell taken from a 3 day old embryo. PGS relies on the fact that chromosomally, this cell should be an identical copy of the remaining cells in the embryo. Following PGS analysis we can then infer that if the cell is normal, it came from a normal embryo, and if it was abnormal it came from an abnormal embryo. A number of studies have shown that some human embryos are not made up of chromosomally identical cells. These embryos are called mosaic embryos, and mosaicism can affect the reliability and hence the benefits of PGS.

This study aims to analyse the chromosomes from all the cells from non-transferred human embryos. This will allow us to investigate the incidence of mosaic embryos and to determine whether mosaicism is linked with a specific patient profile, such as age or IVF techniques such as embryo freezing. This will ultimately improve the management of patients requesting PGS.