Causes & Treatment

How Does an Embryologist Select the Best Embryo(s) for Transfer?

Victoria Wigley  |   10 Apr 2023

Knowing what embryologists look for in embryos and what makes the “best embryos” can be helpful to know when you’re having fertility treatment. Having this knowledge allows you to ask questions to your fertility specialist and embryologist and will support your understanding of their (at times) complex explanations.

Here, The Ribbon Box speaks with Victoria Wigley, Founder of All about Embryology to answer your questions about embryos and embryo transfer.

Victoria is a state-registered Clinical Embryologist with 14 years of clinical experience. Using her experience and expertise, Victoria gives patients independent embryology advice and support through their fertility journey. Click here to book an initial consultation.

Read on to have your embryo-related questions answered.

Over to Victoria…

Firstly: What is Embryology?

Embryology is an area of science related to the formation, growth, and development of an embryo. An embryo is created when the female oocyte (‘egg’) is fertilised by the male sperm, and the subsequent division of the cells to form the embryo. For many years, research centres have studied the creation of animal embryos in vitro (outside of the body), and this led to the first human baby being born from in vitro fertilisation (IVF) just over 40 years ago.

What Makes a Good Embryo?

Great question! When the embryologist is assessing the embryos, they look at several factors to define a “good embryo”. Strict checkpoints within the cell’s division across the first few days of development are a good starting point and an embryo that is dividing too slowly or too quickly could, in turn, be detrimental to the embryo’s subsequent development.

The level of fragmentation caused by each cell division is also key. A high level of fragmentation between the cells is an indicator of poor prognosis. The evenness of cell sizes is also considered at this stage.

As the embryo progresses further, one of the most important things an embryologist will look for is whether the embryo has made the transition from cleavage stage to blastocyst. Only 50% of embryos will make this transition and therefore it is a very important factor when selecting embryos for transfer. The timings of blastulation are also important to consider as earlier blastulation often results in a better developmental potential of the embryo.

Let’s take a look at the stages of embryo development.


What are the Stages of Embryology?

When selecting our embryos, we need to analyse all the different stages of development. The creation of a viable embryo can be broadly classified into three stages. The first stage is fertilisation. This is the union of the female gamete (egg) and the male gamete (sperm) to form a fertilised egg, which is now termed the zygote. This typically occurs within 24 hours after sperm exposure to the egg.

On day 2, the second stage of development occurs; cell division. The fertilised egg divides into two cells and each of these cells divides again, and so on. This is called the cleavage stage of development. By day 3 of development, it is expected that the embryo contains at least 6-8 cells. Prior to each division, the DNA in the cell is duplicated to ensure there is a complete set of DNA in each cell after division – this can help in selecting embryos for transfer.

The final stage of embryo development in the laboratory occurs around days 5-6, and this is blastulation (blastocyst formation). At this stage, the embryo is undergoing huge changes and the cells are differentiating into two distinct cell lines: the inner cell mass and the trophectoderm. The inner cell mass cells are destined to form the baby itself, whilst the trophectoderm cells form all the extra-embryonic material such as the placenta and the amniotic sac.

Who is Embryologist Victoria Wigley?

My name is Victoria Wigley, founder of All about Embryology. I am a state-registered Clinical Embryologist with 14 years of clinical experience. My aim is to use my years of experience and expertise to give patients independent Embryology advice and support through their fertility journey.

​All my consultations can be performed over the telephone. The initial consultation is intended to follow from the patient’s first appointments with the fertility specialist at their chosen fertility clinic. We can discuss in detail their fertility history, including any previous IVF cycles and the outcomes of these where relevant. I can then fully explain the fertility treatments being offered, all the related terminology that will be used, and what to expect in fertility treatment, from the point of egg collection onwards and we can also discuss in detail any embryology treatment add-ons that may have been advised to the patient.

My role will be to better the patient’s understanding of the procedures, and when it comes to add-ons to ensure they fully understand what is being offered, what the potential benefits and risks are, and what the scientific evidence is. Providing all the information in a calm environment can allow the patient to make a genuinely informed decision about their treatment.

Then I will also be able to offer a follow-up consultation service, which can follow at any point from their initial consultation. This may be an opportunity to ask more questions, or to get some further support and guidance throughout or after their cycle.

What Does All about Embryology Offer?

Are you undergoing fertility treatment and are looking to enhance your understanding? Would you like to feel more in control during your consultations and treatment? Maybe you would just benefit from having a friendly professional to guide and advise you through the process?

Infertility can be incredibly difficult for those affected. Over the years, I have seen that many patients just don’t feel comfortable discussing their infertility, even with close family and friends. This can leave them feeling very isolated and vulnerable.

Seeking professional help can be daunting, and even after the initial appointments at a fertility clinic, some patients can come away feeling more confused and overwhelmed than ever. Much of the terminology and treatments discussed can sound like a foreign language, and even with the best professionals in the field, appointment times can sometimes feel limited.

How Does an Embryologist Select the Best Embryos for Transfer?

There is so much that goes into selecting the embryos for transfer. If a patient has an IVF/ICSI cycle, it is the role of the embryologist to handle, monitor and care for the patient’s gametes (the eggs and sperm) and the developing embryos in the lab for around a week. This allows the embryologist to assess each embryo’s individual developmental potential which could lead to a pregnancy.

Once the division occurs on days 2 and 3 of development, the embryo can then be graded by cell number and quality. The grading systems in place help the embryologist identify the stronger embryos in the cohort. To grade the quality at the cleavage stage, we primarily look at the level of cell fragmentation within the embryo, the evenness of the cells and the granularity within the cells. Embryo grading is currently the best, non-invasive way of assessing the embryos on a day-by-day basis and in certain patients, it may also be applicable to test the chromosomes within the embryo to help with the selection process.

As the embryos progress further, one of the most important things an embryologist will look for is whether the embryo has made the transition from cleavage stage to blastocyst. Approximately only 50% of cleavage stage embryos will make the transition to the blastocyst stage.

The grading at the blastocyst stage focuses on the expansion of the blastocyst i.e. how advanced it is, and then the quality of each of the two cell lines (the inner cell mass and the trophectoderm). With the inner cell mass, we are looking to see a compact ball of cells to get the best grading score. With the trophectoderm cells, we are looking for a good cell number and uniform distribution and evenness of these cells around the outside of the blastocyst. The timings of blastulation are also important to consider as earlier blastulation often results in a better developmental potential of the embryo.


Is There Anything I can do to Create Top-quality Embryos?

This is a very tricky question and one that is frequently asked within fertility clinics. Unfortunately, there is often not a great deal that patients can do to create better quality embryos, particularly if we have already seen poor quality embryos in the lab. The embryo quality is often pre-determined, especially from the female side.

Having said that, we always recommend that our patients have themselves and their bodies in the best possible place before starting their fertility treatment cycle, as there are many factors that can be detrimental to the environments that the gametes are developing within. This means both the male and female should be focusing on maintaining a healthy weight, eating the right food groups, regularly exercising, reducing alcohol consumption and smoking, and reducing stress levels where possible. There are also many fertility conception supplements to ensure the patient has adequate levels of all the important vitamins, minerals and antioxidants.

Thank you, Victoria, for sharing your expert knowledge about embryology.

Book an initial, 60-minute consultation with Victoria here.

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