At the beginning, there was an egg… In this promising way, Małgorzata Wójt and Agata Olborska from the Embryology Lab at Salve Medica
begin their presentation on embryo grading and quality assessment. They go onto help us understand all the complicated terms and the results from the area of embryology that are so crucial in the success of IVF procedures.
Oocyte quality importance
The egg (or oocyte in the medical nomenclature) is the most important factor in embryonic development. It may be that the good looking oocyte does not always turn into a good blastocyst. There are different reasons for this which could involve the quality of semen and genetic competence of the embryo itself. However, Małgorzata Wójt admits, the better the oocyte, the higher the blastocyst quality. When it comes to the abnormal oocyte, it almost always results in a poor embryo and poor development to the stage of a blastocyst.
Ferilisation – day 1st
On the first day after correct fertilisation or ICSI, we observe that the oocyte has two polar bodies and two pronuclei. For embryologists the most important is the nucleoid – a small structure inside the nucleoli. Its structure and distribution inside the nuclei is crucial for embryo development. According to Małgorzata Wójt, the first day is important as afterwards it is not possible to assess fertilisation abnormalities. And abnormal fertilisation gives genetic disturbance. Genetically disturbed embryos can develop to healthy looking blastocysts but they will not give birth to a healthy baby.
In order to support their work, embryologists use a time-lapse system. It’s a modern incubator with a built-in camera and software to collect a lot of data during the embryo culturing. Time-lapse embryo monitoring enables continuous and non-invasive embryo observation without the need to remove the embryo from the optimal culturing conditions. It gives embryologists more information. For example, it allows for more accurate morphological assessment and helps in identifying embryos with a higher implantation potential.
Embryo day 3
Then Agata Olborska takes us to day 3 when we encounter a cleavage stage embryo. Quality assessment of day 3 embryos is important to select the top-quality embryo for the transfer. The assessment is based on cell number and cell morphology. It’s important for a patient to know that different laboratories use different assessment standards.
You may be interested in reading more about: Day 3 vs. day 5 embryo transfer success rates
Embryo scoring system
The most common scoring assessment for the blastocyst stage is developed by Gardner and Schoolcraft. It is based on two main criteria: the expansion state of the blastocyst and the consistency of the inner cell mass and the trophectoderm cells. The grading scale in the blastocyst stage embryo assessment has 3 degrees, from A which is the best to C – meaning the worst. We can also distinguish 4 main expansion states of the blastocyst: the early blastocyst (1), the blastocyst (2), the full blastocyst (3) and the expanded blastocyst with the thin zona pellucida (4). If the blastocyst begins to hatch – free itself out of the zona pellucida – we can describe two more grades: the hatching blastocyst (5) and the hatched blastocyst (6).
Another way of assessing embryos is sequential assessment. After 18-19 hours following ICSI, embryologists assess the presence and quality of pronuclei. The embryo that is 25-26 hours after ICSI should be cleaved into two cells. After 42-44 hours, there should be at least 4 blastomers visible in the embryo while 66-68 hours after ICSI, this number should go up till 8. When 90-92 hours have passed since ICSI was performed, the embryo should be at the morula stage. After 106-108 hours – it reaches the blastocyst stage.
Agata Olborska emphasises that an embryo assessment provided by an embryologist is key to choosing the best embryo to transfer. However, embryologists should refrain themselves from crossing out the chance for the blastocyst stage due to the less than perfect embryo development.
Embryo day 5
Finally, Małgorzata Wójt asks the most significant question that all embryologists ask – is it better to transfer embryos on the cleavage stage or on the blastocyst one? The answer seems to be simple: performing blastocyst transfer is more beneficial as the morphologic assessment of day 3 embryo has limited predictive value for subsequent embryonic development. Maintaining the embryo culture until day 5 allows for the correct identification of the best quality embryos. This, in turn, results in the highest probability of implantation success.
You may be interested in reading: Embryo development in IVF Lab – a complete guide written by an embryologist
The presentation and answers to all the questions from attendees were given by experts:
- Agata Olborska – Junior embryologist at Salve Medica and working in the clinic for more than two years. Graduated from the Division of Medical Analytics at the Faculty of Pharmacy at the Medical University of Łódź. The member of ESHRE.
- Małgorzata Wójt – Head of the embryological laboratory at Salve Medica with 18 years of experience in the field of fertility.
She specializes in assisted reproduction procedures. She completed a series of training and workshops in Poland and across the world including the ESHRE certificate of Senior Clinical Embryologist, which entitles the clinical embryologist to practice in all European countries.