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Thursday, 12 October 2023 08:23

How to Select the Best Embryo? Unraveling the Intricacies of IVF Embryo Grading

Embarking on the journey towards parenthood through In Vitro Fertilization (IVF) is both exciting and a tad overwhelming, especially when faced with intricate details like IVF embryo grading. You might have heard this term from your fertility specialist and wondered, "What does it mean to grade an embryo? And how does it influence my IVF success?" Worry not! This guide, crafted in a light and casual tone, will walk you through the essentials of IVF embryo grading without the scientific jargon.

Understanding Embryos and Their Potential

To set the stage, let’s gently dive into what embryos are and why they’re graded. In the context of IVF, embryos are the result of fertilizing an egg with sperm in a specialized lab. These little bundles of cells have the potential to develop into a baby. But here’s the catch: not all embryos have the same potential to result in a healthy pregnancy, and this is where grading comes into play.

Demystifying IVF Embryo Grading

Embryo grading is like a report card for embryos, providing insights into their quality and potential to develop into a healthy fetus. Specialized IVF experts assess various aspects of the embryo, offering them a grade that hints at their viability. However, remember that a lower grade doesn’t automatically discount an embryo’s potential to result in a healthy, successful pregnancy.

Navigating the Day-3 Cleavage Stage Embryo

Embarking on day 3, the embryo enters the cleavage stage, a pivotal point where the cells within are in a state of active division, yet the size intriguingly remains analogous to an unfertilized egg. Here, the embryologist plays a crucial role, in evaluating the morphology or structure and assigning a grade based on two vital parameters: the number of cells and their appearance.

Peering into the Cleavage Stage

The cleavage stage is particularly intriguing, with the number of cells serving as a significant indicator of the embryo’s potential. An ideal day-3 embryo typically parades between 6-10 cells. While an embryo with eight or more cells stands a higher chance of navigating toward successful pregnancy, it’s worth noting that embryos with a modest 3-6 cells can also blossom into healthy fetuses.

The Aesthetics of the Embryo’s Cells

Assigning a grade based on the embryo’s cellular appearance can be a complex affair, subject to each embryologist’s perspective, and is graded from A to D, with A dazzling as the pinnacle of grades. High-grade embryos flaunt cells of a fairly uniform size and exhibit less than 20% fragmentation. Here, fragmentation refers to the shedding of cytoplasmic content from the dividing cells, where excessive loss can potentially hinder optimal cellular function.

Moreover, embryologists cast their gaze upon additional factors, such as:

  • Compaction: Observing whether there’s evidence of cell compaction - a phenomenon where cells adhere tightly to one another, typically unfolding on day 4, signaling readiness for the ensuing stage of blastocyst formation.
  • Cytoplasmic Pitting: Investigating the presence of indentations or depressions within the cell contents, though this area necessitates further research.
  • Vacuoles: Identifying the existence of fluid-filled pockets within the cells.

In a nutshell, an ideal day-3 embryo should boast eight cells, a Grade 1 appearance, and harbor less than 20% fragmentation, weaving a tapestry that signals a promising journey ahead.

Journeying into Day 5: The Blossoming Blastocyst

As we navigate to day 5, the embryo, now referred to as a blastocyst, unveils key developmental milestones. The Inner Cell Mass (ICM) and the Trophectoderm Epithelium (TE), which will forge the path for the fetus and the placenta respectively, begin to take form. Additionally, the Zona Pellucida (ZP), the embryo's protective outer layer, braces itself to break open, signifying readiness for the crucial step of implantation in the uterus.

Grading the Day-5 Embryo: A Closer Look

The grading system for Day-5 embryos is meticulously woven, focusing on three pivotal aspects: the expansion of the blastocyst, the quality of the ICM, and the TE. The blastocyst expansion is assessed based on the volume of the blastocoel (fluid-filled cavity) and the condition of the ZP, while the ICM and TE qualities are gauged based on the cellular integrity and arrangement.

Unfolding the Expansion of the Blastocyst Stage

Navigating through the realm of the blastocyst stage, our attention is captivated by the blastocoel, a cavity brimming with fluid within the embryo, which undergoes a meticulous grading from 1 to 6. Each number provides a snapshot of its expansion journey:

  • Grade 1: Termed as the early blastocyst, the blastocoel takes up less than half of the embryo’s volume.
  • Grade 2: The blastocoel generously expands, occupying more than half of the embryo.
  • Grade 3: The full blastocyst is achieved, with the blastocoel completely enveloping the embryo.
  • Grade 4: The expanded blastocyst showcases a blastocoel larger than the embryo, with the ZP (Zona Pellucida) gracefully thinning.
  • Grade 5: The hatching blastocyst reveals the TE (Trophectoderm Epithelium) making its initial breakthrough through the ZP.
  • Grade 6: The hatched blastocyst sees the TE fully emerge through the ZP.

Diving into ICM Quality

The ICM (Inner Cell Mass), a crucial cell cluster within the blastocyst, destined to form the fetus, is assessed with a grading scale of A to C:

  • Grade A: The ICM boasts numerous, well-defined, and tightly packed cells, signaling a robust potential for implantation and fetal development.
  • Grade B: Here, the cells might be somewhat loosely packed or slightly less defined.
  • Grade C: The ICM reveals fewer cells or perhaps a bit disorganized, whispering a lower potential for successful implantation.

Unraveling the Quality of TE

The TE, the outer cellular layer of the blastocyst that will transform into the placenta and other pivotal pregnancy-supporting tissues, is also appraised with an A to C grading system:

  • Grade A: Numerous tightly packed cells indicate a robust potential for successful implantation and development.
  • Grade B: Cells may be loosely conjoined.
  • Grade C: Fewer cells and a somewhat poorly formed layer hint at a lower potential for successful implantation.

An embryo graded 5AA on day 5 indicates a scenario where the TE is dynamically piercing through the ZP, accompanied by a tightly packed ICM and TE, alluding to an embryo with a stellar potential for successful implantation and onward development.

Decoding the Combinations

Embryo grading unveils a myriad of combinations, especially when we gaze upon the non-degenerated blastocysts, presenting us with nine potential grade combinations: AA, AB, BA, BB, AC, CA, BC, CB, and CC. But what do these combinations tell us about the embryo’s journey?

The essence of this scoring matrix is to act as a compass, guiding specialists in selecting embryos that whisper promises of high implantation potential, thereby enhancing the probability of favorable reproductive outcomes. It’s a strategic method to usher embryos, which are more likely to be euploid, into the spotlight of selection.

An exciting tidbit here is that while certain scores like AA are hailed as superior, indicating an optimum implantation potential, and AB is perceived as preferable compared to AC, every embryo carries a unique potential. These scores are not rigid dictators of success but merely guideposts illuminating the path of embryo selection with the aim of elevating the likelihood of achieving a successful IVF journey.

Parsing Through Pregnancy Success Rates

Forecasting pregnancy success rates through embryo grading might seem like a straightforward pathway, but it's punctuated with nuances and variabilities. For example:

  • Embryo Evolution: Post initial grading, embryos can continue to evolve. An ICM initially graded C may sprout and ascend to a grade A within a day, illustrating that embryo development is a dynamic, ever-changing landscape.
  • Grades and Guarantees: Higher grades might be associated with better pregnancy rates and more live births, yet lower grades do not necessarily spell out a lack of successful outcomes or healthy births.
  • Variables and Uncertainties: While embryo grading provides a lens through which certain aspects of embryo quality can be assessed, it does not encompass all factors influencing successful implantation and pregnancy, presenting a spectrum of variabilities and uncertainties.

Embryo grading, while a pivotal tool, is not a solitary predictor of IVF success. It’s essential to encompass personal circumstances, wield a shield of optimism, and harbor a spirit of hopefulness throughout the IVF journey.


Navigating through the nuances of IVF embryo grading can be complex, but understanding these essentials brings clarity to your IVF journey. While grades are pivotal, they're not the sole predictor of success. So, embrace the process, stay hopeful, and remember: every embryo, regardless of its grade, brings the miraculous potential of life.

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Under Ukrainian law, surrogacy is a legal affordable option for traditionally married couples to have children using their own embryos, or with either an egg or sperm donor. There must be a medical reason you can’t carry a child. You are also able to participate if you have had 4 unsuccessful IVF attempts.


Under Ukrainian law, surrogacy is a legal affordable option for traditionally married couples to have children using their own embryos, or with either an egg or sperm donor. There must be a medical reason you can’t carry a child. You are also able to participate if you have had 4 unsuccessful IVF attempts.