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Dna double helix molecules and chromosomes , Gene mutation , Genetic code , 3d illustration

Pre-Implantation Genetic Testing (PGT-A)

Pre-implantation genetic testing for aneuploidy (PGT-A) is a genetic screening test that gives information about your embryo's genetic health to help us select the embryos with the most potential for transfer to improve your chance of achieving a successful pregnancy.

The first cell of an embryo is made up of a set of chromosomes from the sperm and another set from the egg. If the cell doesn’t have the right number of chromosomes, this can lead to implantation failure or miscarriage. PGT-A allows us to analyse the cells from an embryo to check for the correct number of chromosomes before they’re transferred to the womb.

By using PGT-A, our embryologists have up to a 98% chance of identifying embryos with abnormalities before transfer. Embryo selection can help improve IVF success rates and reduce both the chance of multiple pregnancies and the likelihood of miscarriage.

Main benefits

PGT-A testing can help identify the embryos with the most potential to result in a successful pregnancy. PGT-A testing can’t change the number of viable embryos available for transfer but, by transferring only those that have the correct number of chromosomes, the time taken to establish a pregnancy can be shorter and the distress of failed IVF treatment and risks of miscarriage can be reduced.

Where patients have undergone multiple rounds of IVF and have no explanation for the treatment failure, PGT-A testing can sometimes provide answers and help with decisions about future treatment options.

Care’s own data shows that by performing PGT-A and transferring euploid embryos clinical pregnancy rates (CPR) are increased. In the year to 30 September 2019 Clinical Pregnancy Rate per embryo transferred across patients of all ages following PGT-A was 49%[1]compared with 38% [2] in non PGT-A cycles.

[1]Based on 573 single per euploid embryo transferred resulting in 281 pregnancies with a foetal heartbeat.

[2] Based on 2645 per embryo transferred resulting in 1016 pregnancies with a foetal heartbeat

Benefits for Care patients

  • A clear and straightforward pricing approach which makes PGT-A more cost effective
  • Time lapse imaging with Caremaps-AI is included.
  • Specially trained doctors and genetic counsellors to provide you with specialist PGT-A advice

Who can benefit from Pre-implantation Genetic Testing (PGT-A)?

PGT-A is suitable for all patients, but in particular:

  • People who want to achieve a quicker route to pregnancy
  • Patients who have experienced recurrent miscarriages of unknown cause or anyone who has been through previous unsuccessful IVF treatment
  • A high number of people who have been in the position where they feel that their only option is to give up and then have PGT-A, in many cases they manage to have a baby

In addition:

  • Where the female partner is 36 years of age or older
  • Patients who have had a previous child or pregnancy diagnosed with a chromosome abnormality
  • Patients who produce many embryos and want to ensure transfer of an embryo of known chromosome status to optimise chances of success (we know that up to 50% of embryos in any one cycle may be chromosomally abnormal)

What is PGT-A and how is it performed at Care?

Following fertilisation, an embryo divides into 2 cells, then four, eight, sixteen and so on, until 5 or 6 days after fertilisation there are over 100 cells.  At this stage the embryo is known as a blastocyst and it has an outer layer of cells called the trophoblast which surround the outside of the embryo. These are the cells that develop into the placenta. There is also a ball of cells inside the trophoblast called the inner cell mass and it is these cells that develop into the foetus and then baby.   In PGT-A, approximately 5 cells are removed from the outer layer of the blastocyst.  This procedure, called a biopsy, is performed by a highly skilled senior embryologist.  Biopsied embryos are then cryopreserved (frozen) and the biopsied cells are sent to a specialist laboratory for PGT-A analysis.

The results of the PGT-A test are available within a few weeks. If the biopsied cells have 46 chromosomes, the embryo they came from is considered euploid and the transfer of these embryos can take place in a frozen embryo replacement cycle. Where the biopsied cells had fewer or more that 46 chromosomes, the embryo they came from is considered aneuploid and the embryos are not used in treatment. Occasionally, the results are more complex to interpret and, in these cases, Care has access to expert genetic counselling services to help patients decide whether to transfer an embryo or not.

Studies have shown that removal of cells from the blastocyst doesn’t harm the embryo’s development and thousands of babies have been born after transfer of embryos that were biopsied.

What does PGT-A involve?

Usually our embryologists choose embryos for transfer based on the way they look and develop. This certainly does work, but PGT-A lets us go deeper, allowing us to analyse the genetic makeup of embryos and check that they have the right number of chromosomes before they’re transferred to the womb.

By using PGT-A our embryologists can single out embryos with abnormalities before transfer.

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

This means the embryo is genetically balanced with 46 chromosomes. These embryos can be transferred.

Aneuploid embryos aren’t genetically balanced and have too few, or too many, chromosomes. We won’t transfer these embryos, as they’re more likely to result in failed treatment or miscarriage.

Some embryos may have both chromosomally normal and abnormal cells or a mixture of the two – they are  known as mosaic embryos. The biopsy may take cells that are all abnormal or all normal. The presence of mosaicism can lead to false positive or false negative PGT-A results but is identified in fewer than 9% of cases.

In fewer 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.

The PGT-A Process

IVF

Embryos are produced through an IVF cycle

Embryo biopsy

At 5-6 days after fertilisation embryos should reach the blastocyst stage. Blastocysts contain approximately 100 to 200 cells arranged into an inner cell mass and an outer ring of cells called the trophectoderm. The inner cell mass is made up of undifferentiated stem cells that will go on to form the foetus. The trophectoderm is a layer of cells that will become the placenta. A few trophectoderm cells are carefully removed by our embryologists and sent to the genetics laboratory for assessment, while we freeze your embryos and keep them safe.

Embryo freezing

We are very experienced in freezing and thawing of embryos, we use a process called ‘vitrification’. Vitrification involves much more rapid cooling than other less advanced methods of freezing, and it prevents ice crystals from forming. This preserves the quality of the cells and improves the chances of success when they are thawed. Vitrification has greatly improved the success of embryo freezing and it’s now a very reliable practice.

PGT-A

Testing is carried out using cutting-edge technology to analyse the number of chromosomes present within the embryo's cells.

Embryo transfer

Embryos which are identified as having the correct numbers of chromosomes and therefore most likely to result in a healthy baby are selected for transfer, or we can freeze your embryos for future use.

What are the risks of PGT-A and blastocyst biopsy?

The independent regulator of fertility treatment, the Human Fertilisation and Embryology Authority (HFEA), has developed a ‘red-amber-green’ rating system to provide information about treatments that are offered on top of your routine fertility treatment – known as treatment add-ons. They consider that the only way to be confident that a treatment is effective enough to be used routinely is to carry out a randomised controlled trial (RCT). In an RCT, patients are assigned randomly to two groups: a treatment group, given the new treatment and a control group, given either a well-tried treatment or a placebo.

The HFEA has given PGT-A a red rating because it considers that there is no evidence from such trials that PGT-A increases the overall chances of having a baby. There is information on the HFEA website about PGT-A that you may find useful to consider.

Care did participate in a large scale RCT called the STAR trial, which was published in December 2019. This trial concluded that there was a significant increase in pregnancy rate in a subset of women aged 35–40 where they had more than two embryos available for testing,although overall in all age groups there was no increase in ongoing pregnancy. However, we recognise that that more robust clinical and laboratory trials are needed to prove whether or not PGT-A significantly increases live birth rates.

Although testing is generally very accurate, PGT-A testing may result in a false positive or false negative result in around 3% of cases. In the case of a false positive result, an embryo that may have implanted and developed may be discarded. In the case of a false negative result, an embryo with more or fewer than 46 chromosomes may be transferred.

It is very likely that following PGT-A testing there will be fewer embryos available for transfer or future use as we do not transfer any embryos with an incorrect number of chromosomes - these embryos would not have developed into a successful pregnancy.

Some embryos may have both chromosomally normal and abnormal cells or a mixture of the two – they are known as mosaic embryos. The biopsy may take cells that are all abnormal or all normal. The presence of mosaicism can lead to false positive or false negative PGT-A results but is identified in fewer than 9% of cases.