Embryo screening is a procedure carried out to test whether embryos have any problems with their chromosomes. It is fairly common for abnormal chromosomes to occur very frequently even during normal production of eggs, sperm and during embryo development. In the normal course of events, genetic abnormalities of this nature generally result in an early miscarriage or a failure of the fertilised egg to implant in the womb. The purpose of pre-IVF screening tests is to check for abnormalities before implantation takes place, thus minimising the risk of a miscarriage and maximising the likelihood of a successful pregnancy.
In the context of assisted reproduction, the type of screening known as preimplantation genetic screening is just one of a number of genetic screening techniques that have been developed, particularly in conjunction with those of in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI). In this article we aim to answer the question of what is embryo screening in order to help you decide whether it is right for you.
When are genetic screening techniques used?
Embryo screening is often recommended for naturally occurring pregnancies in women who are over the age of 37, have a family history of chromosome problems, or have had multiple miscarriages. Various methods including the chorionic villus sampling test and the amniocentesis test can be used to test for hundreds of genetic conditions. In this article, however, we are going to focus on the use of embryo screening during the course of assisted reproduction.
At IVI we use embryo screening as part of the IVF Genetic (IVI plus PGT-A) process. After egg retrieval has taken place and the ovocytes have been combined with the sperm to allow fertilisation to take place, embryos are cultured in the laboratory for a number of days. After selecting the most viable embryos based on observation of their morphology, preimplantation genetic screening (PGT) is carried out in order to select the healthiest. The healthiest embryo is then transferred into the uterus using a catheter specially designed for the procedure. This is a simple, painless process after which the patient is able to return home just a few minutes later.
Preimplantation genetic screening at IVI results in higher success rates; selection of the best embryos through PGS improves the chances of implantation, increasing the rate of resulting pregnancy to 70%. The screening also leads to a shorter waiting period between the moment you begin the process and when you achieve a successful pregnancy, since the higher success rate often means avoiding more than one cycle of treatment. Because only healthy embryos are transferred, there is also a lower risk of miscarriage and increased likelihood of having a healthy baby.
How does embryo screening work?
There are two types of screening that can be carried out as part of the IVF process. Preimplantation genetic test for aneuploidies (PGT-A) screens for any chromosomal abnormalities that may be present, while other preimplantation genetic tests (PGT) checks for specific conditions such as Down’s syndrome, Huntington’s disease and muscular dystrophy, among others. In fact PGT can now be used with IVF to test for nearly 400 rare genetic conditions, including cystic fibrosis and early-onset Alzheimer’s. In both of these pre-IVF screening tests, the woman’s eggs are harvested and fertilised. As the testing is carried out on fertilised eggs, neither PGS nor PGD is invasive or painful. A biopsy is carried out on the ‘pre-embryos’ and each chromosomal pair is investigated.
The pre-embryo biopsy is performed on the third day after fertilisation when the pre-embryo has 6–8 cells. The process consists of extracting one or two cells from the pre-embryo, without compromising its normal development in any way. Once the biopsy has been performed, the pre-embryos are put back into the incubator where they stay until the results of the diagnosis are obtained and the possibility of transferring them has been fully assessed.
In the case of PGT, genetic characterisation tests are carried out on patients who are potential carriers of an abnormality, in the preliminary phases of the process. These tests help medical experts gather as much information as possible before proceeding with the PGT.
These processes allow the medical team to identify and circumvent issues which may, without the screening, have prevented pregnancy or resulted in miscarriage; thus the likelihood of an IVF cycle working is significantly increased. Once the pre-IVF screening tests have been completed, the IVF process continues in the normal way. Only embryos that have been cleared in the tests are selected to be placed into the patient’s uterus, where they will develop as normal.
Over the past decade genetic screening techniques have become more comprehensive, from the ability to examine just nine chromosomal pairs in 2006 to being able to investigate all 23 pairs in 2018. As a result, more than ever before, the procedure yields a result that allows patients and their medical teams to make the most well-informed choices in their individual circumstances.
A further advantage of these genetic screening techniques is that following treatment, all unused good quality embryos will be cryopreserved for possible future use, therefore avoiding the need to undergo a new stimulation cycle if the patient wishes or requires a subsequent treatment.
You can check out our website to learn more details about these tests, and to familiarise yourself with other potential benefits of preimplantation genetic screening for IVF.
Who is embryo screening for?
Now that we’ve provided more information about what embryo screening is and what exactly is involved in genetic screening techniques, you may be wondering whom doctors recommended the testing for. Embryo testing and treatments are designed to help people who have serious inherited diseases in their family and want to avoid passing the condition on to any children they might have. If you or a family member have a serious genetic condition, you may wish to have your embryos screened during IVF in order to ensure that only healthy embryos are implanted in the womb.
The most frequent use of these genetic screening techniques is for women who have had multiple miscarriages or failed IVF cycles and who would like to test the embryos for any problems that could potentially lead to another failed treatment. PGS is also recommended for cases in which there are abnormalities in spermatozoa meiosis, and for women whose age makes them more prone to reproductive genetic problems. PGD is particularly recommended for patients over the age of 40 who intend to use their own eggs instead of donor eggs.
Is embryo screening right for me?
Women considering IVF will naturally need to consider whether embryo screening is the right course for them to take. If any of the conditions are categories described above apply to you, you may find it helpful to watch our video about IVF to familiarise yourself more with the process and learn what to expect. When you or you and your partner have a major life decision to consider, it is always advisable to gather as much information as you can through videos such as this and by reading up on the subject. If you are having any doubts about whether embryo screening is right for you, we invite you to make an appointment for a consultation at one of our clinics.
Your medical assessor there will answer any questions you may have and explain anything you would like to know about why this treatment may be recommended to help you fulfil your dream of starting a family. During the course of your first visit to IVI, you can expect a consultation consisting of assessment and diagnosis, followed by a discussion of the treatment recommended to be carried out. If this involves embryo screening as part of the IVF procedure, your consultant will talk you through the steps involved and answer your questions.
We at IVI are world leaders in these techniques, and ours was the first clinic in the world to successfully screen for and intercept a specific chromosomal abnormality through PGD, in 2006. In that first case, a healthy baby was subsequently born to a couple with a high risk of lymphohistiocytosis affecting their offspring. Since then we have continued to research and develop the procedures, making us ideally placed to offer you our advice and expertise.
If at any time you find you have additional questions that you didn’t think of or weren’t able to ask during the consultation, feel free to give us a call and the professionals from the centre will be at your disposal to clarify things for you.