Pre-implantation Genetic Screening
For over twenty years, it has been possible to test embryos for chromosomal abnormalities during an IVF cycle to identify the embryos with the best chance of developing into healthy babies. This process is called Pre-implantation Genetic Screening (PGS). The technique used until recently for PGS is fluorescent-in-situ hybridisation (FISH). Unfortunately, with FISH it was possible to test only a fraction of the chromosomes (up to 10 out of the 23). It has also been shown to sometimes deliver inaccurate results. A new technique called PGT-A is now available to test all 23 chromosomes in a single cell or blastomere.
Up to 40-80% of human embryos may contain abnormal number of chromosomes (known as ‘aneuploidy’), depending on the woman’s age. Most chromosomally abnormal embryos will not implant and if they start to implant are most likely to miscarry. PGT-A makes it possible to screen eggs or embryos so as to select only those chromosomally normal for transfer into the woman’s uterus, thereby potentially improving the chances of successful implantation and reducing the risk of miscarriage.
Who is it for?
PGT-A may be particularly beneficial for women over 35 years of age, couples experiencing recurrent miscarriage or recurrent IVF failure, or women who have had termination of one or more chromosomally abnormal pregnancies.
Preimplantation genetic diagnosis (PGD)
PGD is a laboratory test, performed on eggs or embryos during an IVF cycle, that enables couples to check whether their pregnancy may be affected by a chromosomal disorder or an adverse genetic condition. It can be used to screen for many genetic conditions, including single gene disorders and chromosomal abnormalities. Many couples ask for PGD to test for aneuploidy (such as Down syndrome). It is thought that a large proportion of early miscarriages may be due to aneuploidy, which increases with the age of the female partner. Others wish to test for specific single gene disorders or genetic conditions that run in the family, such as cystic fibrosis or muscular dystrophy. It can also be used to screen eggs and embryos of individuals who carry a chromosomal translocation, significantly decreasing the risk of miscarriage or birth defects.