What is embryo screening and is it right for me?

Written by Dr Fleur Cattrall
06 Oct

One significant development in assisted reproductive technology (ART) in the last 25 years is our ability to remove cells from a developing embryo and perform genetic testing. The procedure is termed preimplantation genetic screening or preimplantation genetic diagnosis depending on its application.

As technology has improved we have seen the use of PGS and PGD in IVF rise, with the latest Australia and New Zealand Assisted Reproductive Treatment Database (ANZARD) reporting a 20% increase.

embryo screening

What is Preimplantation genetic screening?

Preimplantation genetic screening (PGS) or ‘embryo screening’ is a method where embryos from presumed chromosomally normal genetic parents are screened for abnormalities. It involves screening all 24 chromosomes in a developing embryo to select the embryo/s without any chromosomal errors that is most likely to result in an ongoing pregnancy.

PGS is an evolving technique that is now recognised more arguably as a way to improve pregnancy rates in women experiencing repeated IVF failure and recurrent miscarriage.

What is Preimplantation genetic diagnosis?

At this stage of medical science we are not able to routinely ‘screen’ embryos for faults in the 20,000 or so genes located on our 23 pairs of chromosomes. Therefore we cannot tell if an embryo is destined to develop a particular genetically inherited condition unless we are specifically looking for it. This is known as Preimplantation genetic diagnosis - PGD for short. Some couples may require this when there is a known genetic condition that runs in their family, such as Huntington’s disease, Cystic fibrosis, Thalassaemia and Fragile-X.

How is PGS & PGD performed?

Both PGS & PGD involve taking cells from a developing embryo usually at the day 5 (blastocyst) stage. This step is called an embryo biopsy. The biopsied cells are then tested to assess the embryo and health of any potential baby. The embryos are frozen whilst we wait for the results. The embryo then determined to either have no chromosomal errors (PGS) or be of low risk for the genetic condition we are testing for (PGD) is transferred back into the woman’s uterus.

Embryo selection in an IVF cycle

During an IVF cycle, selecting an embryo for transfer has traditionally been based on appearance alone, called morphology.  A ranking of which embryo is likely to result in a baby, based on an appropriate number of cell divisions at a given time is established. Then, each month, the next best embryo is transferred into the woman’s uterus. Unfortunately, many embryos do not result in a baby. The reasons for this are mostly related to genetic factors of the embryo and not the uterine environment.

What causes an embryo transfer to fail?

There are many reasons the transfer of an embryo does not lead to an ongoing pregnancy. An important requirement for an embryo is that it is genetically normal and has 23 pairs of chromosomes, which are labelled 1 to 22. There are also 2 sex chromosomes, XX (female) or XY (male).

Sometimes an embryo can have an extra chromosome, such as three copies of chromosome 21, which we call trisomy 21. This embryo would be destined to have Down syndrome. If an embryo is missing a chromosome, for example chromosome 4, we call this monosomy 4. These major structural errors, also called aneuploidy, commonly lead to a negative pregnancy test or result in miscarriage.

How common is it for an embryo to be genetically abnormal?

We know that approximately 30% of embryos from women aged 30 have genetic errors and this rises to 80% of their embryos at the age of 40. The reason for this is due to the ageing process that inevitably occurs in the egg. 

Women are born with all the eggs they will ever have and as a woman’s eggs get older, these errors become more frequent. Unfortunately, even the best embryos based on their appearance can have these errors. The result is that most of these embryos when transferred will result in a negative pregnancy test or miscarriage. This is largely the reason that the chance of pregnancy declines as women get older. The chance of miscarriage also increases for the same reason. At 30 years, 1 in 6 pregnancies end in miscarriage. At 40 years, this has risen to 1 in 3 pregnancies.

How can embryo screening increase pregnancy rates?

When we identify and exclude abnormal embryos from transfer, the likelihood is that the time to achieve an ongoing pregnancy will be reduced. Fewer procedures and less dreaded two week waits make IVF treatment easier.

It’s important to remember that transferring an embryo without genetic errors does not guarantee a pregnancy. An embryo must also be normal in other ways that we cannot test for.

Who could benefit from embryo screening?

Women recognised to benefit from embryo screening are those experiencing recurrent miscarriage or implantation failure. There is also increasing evidence to support the use of embryo screening for women 38 years and older. 

Since the embryo screening process involves comparing embryos to see which one is more likely to lead to a successful pregnancy, it is more appropriate for couples that have more than two day five (blastocyst) embryos.

What can I do next?

If you have questions about PGS or PGD, consult a fertility specialist. They will be able to advise whether the technique is appropriate for your situation and answer any questions you might have.

Read more about PGS at Virtus Health:  Victoria»  New South Wales»  Queensland»  Singapore»

 

Contact

Make an enquiry

Share this article


We hope this article was informative and useful to you. If you have any questions or feedback, feel free to get in touch at info@blogivf.com.au.



Related Articles

IVF & embryo donation – the gift of a family

With Sofia Vergara, star of the hit TV show Modern Family, reportedly in a battle with her ex-fiancé over the rights to frozen embryos they created while together, the press attention around her situation has thrown issues surrounding stored embryos into the spotlight. A much more common situation, for couples who have had IVF treatment, is deciding what to do with excess frozen embryos after they have completed their family.

For many families, IVF is a life-changing experience – one that helps them realise the dream of a having a baby. As an obstetrician and a mother, I know just how much joy a child can bring to a family, conversely, I know the heartache that comes with not being able to conceive. With Mother’s Day approaching, now is the perfect time for couples with frozen embryos who have completed their family, to consider giving another family struggling to conceive the greatest gift of all.

Why are there embryos left over after an IVF cycle?

Today, about 1 in 23 children in Australia are born as a result of IVF and other assisted reproductive technologies. With IVF success rates continuing to rise, and with treatment becoming considerably more accessible, more couples than ever before are undergoing IVF for a number of medical and social reasons.

An IVF cycle involves a number of eggs being surgically collected from the female partner and fertilised with the male partner’s sperm, before being transferred back into the woman in the hope that she achieves a successful pregnancy and birth. Any remaining embryos are then frozen, allowing for future chances at pregnancy. If the couple have embryos left over after they have completed their family, they are then faced with the dilemma of what to do with those frozen embryos.

What are the options for excess embryos?

The length of time people can store their embryos varies from state to state in Australia, from 5 to 10 years. After that time, the biological mother and father of those embryos must make a decision about what do next – generally this involves donation for research1 or disposal of the embryos.

However, there is another option – donation of the embryos to another family.

Having overcome infertility and the fear they might never have a family, couples with excess embryos have a greater understanding and appreciation than most of just how generous the act of donating their embryos to another couple could be.

Embryo donation does come with complex emotional and psychological implications, so it’s a decision that involves a lot of consideration and counselling. Couples are often concerned about the welfare of the future children born from donated embryos, and consider how they will tell their own children.

What is the process for embryo donation?

If donating stored embryos is something you would like to consider, there are options. You can become a donor for someone you know – a friend, family member, or someone you know through personal networks that might be having trouble conceiving. Alternatively, many fertility clinics (including Queensland Fertility Group, IVF Australia, Melbourne IVF and TasIVF) offer a confidential donor service. It’s worth being aware that generally you cannot donate embryos to another family if they have been created using donor sperm or eggs2. If you are interested in donating your excess embryos, I recommend that you speak to your fertility clinic initially, to find out more about the process, criteria and what counselling and support is offered.

It’s an emotional decision – one that’s full of complexities – but wouldn’t it be an amazing feeling to know you’ve helped one more mother’s dream come true next Mother’s Day?

Find out more:

Embryo Donation in Queensland  
Embryo Donation in NSW  
Embryo Donation in Victoria  
Embryo Donation in Tasmania   
 

1 Research in Australia using human embryos and stem cells is governed by strict guidelines and reviewed by various ethics committees and regulatory bodies. Embryo donation for research purposes may not be available for embryos created from donated gametes or for QFG patients.

2 At Melbourne IVF, embryos that have been created using donor eggs and/or sperm may be donated to another person or couple, although only after ethics committee approval has been obtained. 

What is embryo screening and is it right for me?

One significant development in assisted reproductive technology (ART) in the last 25 years is our ability to remove cells from a developing embryo and perform genetic testing. The procedure is termed preimplantation genetic screening or preimplantation genetic diagnosis depending on its application.

As technology has improved we have seen the use of PGS and PGD in IVF rise, with the latest Australia and New Zealand Assisted Reproductive Treatment Database (ANZARD) reporting a 20% increase.

embryo screening

What is Preimplantation genetic screening?

Preimplantation genetic screening (PGS) or ‘embryo screening’ is a method where embryos from presumed chromosomally normal genetic parents are screened for abnormalities. It involves screening all 24 chromosomes in a developing embryo to select the embryo/s without any chromosomal errors that is most likely to result in an ongoing pregnancy.

PGS is an evolving technique that is now recognised more arguably as a way to improve pregnancy rates in women experiencing repeated IVF failure and recurrent miscarriage.

What is Preimplantation genetic diagnosis?

At this stage of medical science we are not able to routinely ‘screen’ embryos for faults in the 20,000 or so genes located on our 23 pairs of chromosomes. Therefore we cannot tell if an embryo is destined to develop a particular genetically inherited condition unless we are specifically looking for it. This is known as Preimplantation genetic diagnosis - PGD for short. Some couples may require this when there is a known genetic condition that runs in their family, such as Huntington’s disease, Cystic fibrosis, Thalassaemia and Fragile-X.

How is PGS & PGD performed?

Both PGS & PGD involve taking cells from a developing embryo usually at the day 5 (blastocyst) stage. This step is called an embryo biopsy. The biopsied cells are then tested to assess the embryo and health of any potential baby. The embryos are frozen whilst we wait for the results. The embryo then determined to either have no chromosomal errors (PGS) or be of low risk for the genetic condition we are testing for (PGD) is transferred back into the woman’s uterus.

Embryo selection in an IVF cycle

During an IVF cycle, selecting an embryo for transfer has traditionally been based on appearance alone, called morphology.  A ranking of which embryo is likely to result in a baby, based on an appropriate number of cell divisions at a given time is established. Then, each month, the next best embryo is transferred into the woman’s uterus. Unfortunately, many embryos do not result in a baby. The reasons for this are mostly related to genetic factors of the embryo and not the uterine environment.

What causes an embryo transfer to fail?

There are many reasons the transfer of an embryo does not lead to an ongoing pregnancy. An important requirement for an embryo is that it is genetically normal and has 23 pairs of chromosomes, which are labelled 1 to 22. There are also 2 sex chromosomes, XX (female) or XY (male).

Sometimes an embryo can have an extra chromosome, such as three copies of chromosome 21, which we call trisomy 21. This embryo would be destined to have Down syndrome. If an embryo is missing a chromosome, for example chromosome 4, we call this monosomy 4. These major structural errors, also called aneuploidy, commonly lead to a negative pregnancy test or result in miscarriage.

How common is it for an embryo to be genetically abnormal?

We know that approximately 30% of embryos from women aged 30 have genetic errors and this rises to 80% of their embryos at the age of 40. The reason for this is due to the ageing process that inevitably occurs in the egg. 

Women are born with all the eggs they will ever have and as a woman’s eggs get older, these errors become more frequent. Unfortunately, even the best embryos based on their appearance can have these errors. The result is that most of these embryos when transferred will result in a negative pregnancy test or miscarriage. This is largely the reason that the chance of pregnancy declines as women get older. The chance of miscarriage also increases for the same reason. At 30 years, 1 in 6 pregnancies end in miscarriage. At 40 years, this has risen to 1 in 3 pregnancies.

How can embryo screening increase pregnancy rates?

When we identify and exclude abnormal embryos from transfer, the likelihood is that the time to achieve an ongoing pregnancy will be reduced. Fewer procedures and less dreaded two week waits make IVF treatment easier.

It’s important to remember that transferring an embryo without genetic errors does not guarantee a pregnancy. An embryo must also be normal in other ways that we cannot test for.

Who could benefit from embryo screening?

Women recognised to benefit from embryo screening are those experiencing recurrent miscarriage or implantation failure. There is also increasing evidence to support the use of embryo screening for women 38 years and older. 

Since the embryo screening process involves comparing embryos to see which one is more likely to lead to a successful pregnancy, it is more appropriate for couples that have more than two day five (blastocyst) embryos.

What can I do next?

If you have questions about PGS or PGD, consult a fertility specialist. They will be able to advise whether the technique is appropriate for your situation and answer any questions you might have.

Read more about PGS at Virtus Health:  Victoria»  New South Wales»  Queensland»  Singapore»

 

Receive our quarterly e-news with free advice from the fertility experts.