PGT-A – Preimplantation Genetic Testing for Aneuploidy

There are multiple reasons why you might consider preimplantation genetic testing of embryos or PGT. PGT-A screens for chromosome changes which may affect any embryos, PGT-SR is used for patients who have a structural rearrangement (translocation) of their chromosomes, and PGT-M is used for patients with a known single gene condition.

The fact is, embryos may look the same under the microscope – even if they do not have a typical number of chromosomes.

Chromosome changes affecting the egg or sperm are a major cause of pregnancy loss either at the time of implantation or during pregnancy. Most of these changes occur in the egg, as the chromosome pairs are not separated until ovulation. This means that eggs are more likely to have missing or extra chromosomes with increasing female age.

Testing for missing or extra chromosomes can help focus your treatment and embryo transfers on those embryos with the highest chance of implantation. It may be considered if you are suffering recurrent miscarriage, are over 35, or if you’ve had repeated unsuccessful IVF cycles. If there are specific chromosome conditions present in the family, our genetic counselling team will discuss what testing may be available for you.

Embryos which have been grown to Day 5 have cells removed from the outside layer of the embryo (“embryo biopsy”) and the cells are sent to the Monash IVF Genetics laboratory for testing. The embryos are frozen while this testing is taking place.

The technology used to analyse the DNA is known as next generation sequencing.

The DNA is amplified to millions of copies from just a handful of cells, and the sequencer then analyses the DNA fragments and compares them to the human genome – the standard map of human genes.

Specialised software is used to work out if there are more or less fragments from each chromosome, indicating that there may be an extra or missing chromosome.

It takes 2-3 weeks to receive the results from this testing, after which your fertility specialist can discuss with you which embryos are most suitable to transfer. The embryos which have a typical number of chromosomes have the highest chance of implantation and successful pregnancy.