Pre-implantation Genetic Testing for Aneuploidy (PGT-A)

Pre-implantation Genetic Testing for Aneuploidy is a technique used to assess the chromosomes of embryos created in an IVF cycle.

Every cell in the body contains DNA, which makes up our genes and these are the building blocks for our chromosomes. The normal human cell contains 23 pairs of chromosomes (46 chromosomes in total). There are 22 pairs of the numbered chromosomes (1-22) and one pair of the sex chromosomes X and Y.

A normal fertilised egg is the start of a human embryo and this contain 46 chromosomes. Half of these chromosomes come from the egg itself and the other half from the male sperm. If the embryo doesn’t have the normal number of chromosomes this is called aneuploidy and will lead to implantation failure and miscarriage.

Embryos created in an IVF cycle are selected for transfer according to how they look and have developed in the lab. PGT-A allows us to look at the number of chromosomes in an embryo before transferring them into the womb. This reduces the chances of transferring embryos with abnormal chromosome numbers.

PGT-A has been researched extensively as it was thought it would change pregnancy rates significantly when it was first introduced. However, the process of PGT-A involves a number of additional steps compared to a standard IVF cycle. Rather than just replacing embryos based on their appearance the embryos are biopsied (a few cells removed), frozen while these cells from the embryo are tested. Once the biopsies cells have been assessed the embryo can then be thawed out and replaced if it known to be normal.

The Human Fertilisation and Embryology Authority (HFEA) is the regulator of licensed clinics and treatments in the UK and advises on additional techniques like PGT-A. It uses a traffic light system to try and help patients understand the evidence behind fertility treatment ‘add ons’. To find out more about IVF ‘add ons’ then take a look at our article on “Add-ons Don’t Always Add up”.

PGT-A has a red warning light from the HFEA as research trials have not yet been able to show that this additional fertility treatment step increases the chance of a pregnancy. It has been shown that it may speed up the route to a normal pregnancy but it is not without risk as removing cells from an embryo (biopsy) and freezing and thawing embryos are not without risk to the embryos.