PGT-A: your embryo results explained

DNA makes us who we are. It contains the genetic information for our development and functioning, and is housed in structures called chromosomes.

Every cell in an embryo should contain 23 pairs of chromosomes – 46 in total. One chromosome from each pair comes from the sperm and one from the egg. As the cells of an embryo divide, the chromosomes are copied so each new cell contains an identical copy of the same 46 chromosomes.

However, around half of all embryos will have an incorrect number of chromosomes. These embryos may fail to develop, will develop in the laboratory but fail to implant, or may implant then miscarry. As these embryos will often look normal when assessed under the microscope, we can assess their potential to develop into a healthy pregnancy through PGT-A testing.


How does PGT-A work?

After fertilization, embryos develop in the lab for 5-6 days, at which point they become blastocysts. In a PGT-A cycle, embryologists will remove a few cells from the outer layer of each blastocyst. We then send these cells to a special laboratory to undergo screening to analyse the number of chromosomes within the cells, meanwhile freezing the embryos.

The results of the PGT-A test are available within a few weeks and will inform how many embryos are suitable for transfer.


What do my PGT-A results mean?

After PGT-A, each embryo will have one of four results:

  • Euploid: these embryos have the correct number of chromosomes. Euploid embryos have much greater chances of implanting successfully, higher chances of successful pregnancies, and reduced rates of miscarriage. These embryos can be transferred.
  • Aneuploid: this means the number of chromosomes observed in the embryo sample was incorrect, they either have extra or missing chromosomes. We won’t transfer these embryos, as they’re more likely to result in failed treatment or miscarriage.

The following are all types of aneuploid result:

  • Monosomy: only one of the chromosomes in a pair are present, one chromosome has been lost in cell division.
  • Trisomy: the embryo contains an extra copy of a chromosome in each cell. A common example of trisomy is Down syndrome, known as trisomy 21 due to there being an extra copy of chromosome 21.
  • Segmental aneuploidy: involves a section of a chromosome, rather than the entire chromosome but still causes an inbalance of genetic material in the cells. The clinical significance of this is hard to predict. Care can provide access to expert advice in cases where the test results require interpretation.
  • Mosaic: these embryos contain a mixture of euploid and aneuploid cells, so different cells in the embryo may have a different set of chromosomes. This occurs when chromosome abnormalities arise spontaneously as the embryo divides. The presence of mosaicism can lead to false positive or false negative PGT-A results but is identified in fewer than 9% of cases. The impact of mosaicism is hard to quantify, but Care can provide you with expert genetic counselling and support to help you decide whether to transfer a mosaic embryo.
  • No result: In less than 5% of cases, we simply won’t be able to tell whether the embryo is euploid or aneuploid. These can still be transferred or, in special circumstances, they might be re-biopsied.


Using PGT-A may mean you have fewer embryos available to use in treatment or for freezing to use in future treatment. Although PGT-A can’t change the number of viable embryos available for transfer, by transferring only those that have the correct number of chromosomes, the time taken to establish a pregnancy can be shorter and the upset of failed cycles and risks of miscarriage can be reduced.


PGT-A 2.0 at Care

At Care, we are increasingly using artificial intelligence (AI) in our treatments. We have introduced a PGT-A platform known as PGTai 2.0 which provides an even greater level of embryo testing to make results more personal. We can now identify if an abnormality arises from the egg or sperm, helping to concentrate efforts to improve quality before starting a new cycle. Or it can help with decision-making when a couple opts to switch to donor eggs or donor sperm for their treatment.


If you would like to use PGT-A in your treatment plan or if you have any other questions, you can contact our enquiries team at 0800 564 2270, we will be happy to help you.


With love from CARE x

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