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.

What is Embryo Screening?

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 fertilized egg to implant in the womb. The purpose of pre-IVF screening tests is to check for abnormalities before implantation takes place. This minimises the risk of a miscarriage and maximising the likelihood of a successful pregnancy.

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.

Who is embryo screening 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. Also 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.

Women considering IVF will naturally need to consider whether embryo screening is the right course for them to take. 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.

Types of embryo screening

At IVI, we offer various types of embryo screening, tailored to different cases and needs.

PGT-A: Test to detect aneuploidies

This test allows the detection of extra or missing chromosomes, numerical abnormalities also known as aneuploidies. Some of the most common include trisomy 21 (Down syndrome), trisomy 18, trisomy 13, 45X (Turner syndrome), 47XXY (Klinefelter syndrome), 47XYY, and 47XXX.

PGT-M: Genetic testing for monogenic (single-gene) disorders

This test detects alterations or mutations in a single gene in embryos, which can lead to a monogenic disorder.

PGT-SR: Testing for structural rearrangements

This test identifies embryos with abnormally structured chromosomes, which can result from the breakage or incorrect joining of chromosome segments. There are various types of these abnormalities: translocations, deletions, duplications, insertions, rings, or inversions, which can be balanced or unbalanced. Various chromosomal structural rearrangements can lead to disease.

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. 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 fertilized. As the testing is carried out on fertilized 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. They will stay there 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.

Process of embryo screening allows 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. This will herefore avoid 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.

What are the Advantages of Embryo Screening?

What are the pros and cons of embryo screening? 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. 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.

Your medical assessor there will answer any questions you may have. He will also 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.

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.