Embryo Quality 101: What Your Clinic Means When They Talk About Size, Grade & Viability
- Kat Thompson
- Oct 8
- 6 min read
Talking about embryo quality during IVF or fertility treatment can feel like entering a different language. You hear things like “Grade A,” “6-cell,” “10% fragmentation,” or “blastocyst expansion”, and it can all feel overwhelming and impersonal. My role, as a Certified Fertility Doula, is to help you understand what those terms really mean, translate them into meaningful insights without shame or blame, and support you emotionally through each step.
Before we dive in, I recommend watching Dr. Rahi Victory’s “Embryo Math” video. It presents how embryologists use numbers and probabilities in decision-making, a helpful visual companion to what we’ll talk about here. (You can treat this blog as a complement, not a substitute for your clinic’s explanations.)
Let’s walk through embryo quality in plain language, spotlight what the lab sees (and doesn’t see), and point out where your own agency and support can matter.
What Does “Embryo Quality” Really Mean?
When your clinic or embryologist talks about “quality,” they are referring to a visual / morphological assessment: what the embryo looks like under the microscope (or via time-lapse imaging).
This assessment is a guide, not a verdict. It helps them choose which embryos might have better odds, but it doesn’t guarantee success.
Importantly, embryo quality is not a reflection of your body, your effort, or your worth. It’s only one piece of a much bigger picture.
As a doula, my reminder to clients is: this is data — information to help navigate choices, not a judgment on you.
The Building Blocks of Embryo Grading (in Everyday Language)
Below are the main features embryologists often assess. Think of them as “clues,” not “rules.”
Cell Number & Timing
In the early days (Day 2, Day 3), embryos are in their cleavage stage, dividing but not yet growing much in size.
For example, by Day 3, embryos with 6-8 cells tend to have a stronger chance of progressing further.
But, caveat: variations in speed don’t always mean doom: some embryos divide slowly yet become healthy blastocysts, and some that divide quickly falter.
Cell Symmetry (Uniformity of Size)
Ideally, the cells (blastomeres) should look similar in size: consistent, balanced divisions suggest smooth development.
Slight variations are perfectly normal. Embryos are living, not machines.
Large discrepancies (one cell much bigger / smaller) may raise caution flags, but don’t automatically disqualify.
Fragmentation
Fragmentation refers to bits of cellular material breaking off or floating between cells (sometimes visible as “pieces” between blastomeres).
Clinics often report a percentage (e.g. “5% fragmentation,” “15% fragmentation”) as part of grading.
In many studies, embryos with higher fragmentation (> 25–50 %) have reduced viability compared to those with low fragmentation.
BUT — and this is important — even embryos with moderate fragmentation have led to successful pregnancies. Fragmentation is a risk factor, not a mandate for failure.
Multinucleation, Vacuoles & Other Irregularities
Sometimes a single cell shows more than one nucleus (multinucleation). That can suggest abnormal chromosome distributions or errors in division.
Vacuoles or dark “bubbles” inside cells, or edges that look irregular, are features that might lower the score. They are morphological clues, not deterministic statements.
Grading / Rank Systems
Clinics often translate observations into grades like A / B / C / D or terms like “good / fair / poor.”
For blastocysts, more structured systems exist (e.g., Gardner scoring: expansion, inner cell mass, trophectoderm).
But here’s a nuance: these grading systems vary by clinic, lab, and embryologist. What’s labelled “good” in one lab might be “average” in another.
So, when your clinic gives you a grade, it’s helpful to ask their internal data: how embryos of that grade have performed historically at their clinic.
Tools Beyond Static Observation
Embryo assessment is becoming more dynamic and data-driven. These are adjunct tools that labs sometimes use (but not always):
Time-Lapse Imaging / Morphokinetics
Instead of snapshots, the embryo is continuously monitored, so embryologists can see when each division happens, how stable it is, and detect subtle abnormalities (like sudden arrests or irregular cleavage events).
These kinetic parameters (timing patterns) can add prognostic value beyond static snapshots.
Genetic Testing (PGT-A / PGS)
Some embryos undergo biopsy of a few cells to test for chromosomal normalcy (euploidy), which gives insight that morphology alone can’t supply.
Note: even a top-grade embryo might harbour chromosomal issues, and conversely, a “less perfect” morphology embryo might be chromosomally normal.
Genetic testing comes with trade-offs: cost, risk of the biopsy, and not all clinics or patients will choose it.
Algorithmic / AI Grading
Emerging tools are using deep learning to standardize embryo grading, reduce subjectivity, and integrate complex patterns (both spatial and temporal).
These tools are promising but not universally adopted yet. They may become more commonplace in the coming years.
What “Size / Expansion” Means (But Also What It Doesn’t)
At the blastocyst stage (usually Day 5 or 6), labs often refer to the degree of expansion (how much the embryo has grown, the hollowing out of the cavity, and the thinning of the shell).
They also inspect the inner cell mass (ICM) (which becomes the baby) and the trophectoderm (TE) (which becomes the placenta).
A more expanded blastocyst with a robust ICM and healthy TE is generally considered favourable.
But, importantly, extremely over-expanded or irregular blastocysts may be less stable; “big” doesn’t always equal “best.”
Think of “size” as one variable in a multi-axis evaluation, not a standalone champion.
How to Read Your Clinic’s Report — and What to Ask
Here’s how to piece together the data the clinic gives you, and what questions might bring clarity and confidence.
Sample Report Terms (and What They May Imply)
“Day 3: 7-cell, Grade B, 10% fragmentation”“Day 5: Blastocyst 4AA (Expansion 4, ICM = A, TE = A)”
The cell number suggests how complete the divisions have been.
The grade / letter gives a shorthand view of overall morphology.
The fragmentation percentage describes what proportion of the embryo looks “broken off.”
For blastocyst grading: expansion number + ICM grade + TE grade indicate several zones of health.
Questions to Ask Your Clinic / Embryologist
What does my clinic’s grading scale mean (in your lab’s history)?
Among embryos with this grade at your clinic, how many have resulted in successful implantation / live birth?
What percentage fragmentation was factored, and how much weight do you assign it?
Did any embryos show signs of multinucleation, vacuoles, or irregular cleavage?
If you use time-lapse imaging or morphokinetics, did my embryo show any alerts?
Was genetic testing recommended or performed, and what were the results (if applicable)?
How does your lab “rank” embryos when choosing which to freeze, biopsy, or transfer?
I can help you translate lab reports into plain language, coach you on which questions matter, and support you emotionally through the waiting and decision-making moments.
Limitations, Realistic Perspective & Where You Do Have a Say
Limitations of Embryo Grading
The assessment is probabilistic; it gives odds, not guarantees.
Many high-grade embryos don’t succeed; many lower-grade ones do.
Grading doesn’t capture everything going on inside the embryo (like mitochondrial health, epigenetics, or subtle molecular dynamics).
Success also depends on the uterine environment, timing, transfer technique, and chance.
Where You Can Have Influence
Choosing a clinic / lab with strong embryology standards and transparency.
Asking for clear, patient-friendly reports and explanations (I can help you prepare questions).
Engaging in holistic support (stress reduction, emotional care, sleep, nutrition), while acknowledging that none of this “guarantees” embryo morphology, it helps your overall health and sense of agency.
Building a support system: mental, emotional, relational — so you’re not navigating this alone.
Emotional Compassion
It’s natural to feel anxiety, disappointment, and confusion.
Grades and numbers are not judgments on your body or identity.
Part of being a fertility doula is helping you carry the emotional weight, helping you recontextualize data, and supporting resilience when results aren’t what you hoped.
Knowledge + Compassion = Empowered Navigation
Embryo quality reports can feel overwhelming, like you’re handing over your hopes to a lab report. But my invitation to you is this: let these reports inform choices, not define destiny.
Watch Dr. Victory’s “Embryo Math” to see how probabilities map to real decisions.
Ask your clinic (or let me support you in asking) clear, grounded questions rooted in your values.
Lean into emotional and holistic support; science and heart can coexist, and both matter.
As your doula, my role is to walk with you, helping you interpret, process, ask, grieve, hope, and keep moving forward with clarity and care.
Every fertility journey is deeply personal — full of data, decisions, and emotions that deserve space to breathe. As a Certified Fertility Doula, I offer compassionate, non-clinical support to help you navigate IVF or trying to conceive (TTC) with clarity, calm, and confidence. Together, we’ll turn the complex into understandable, the overwhelming into manageable, and the process into one where you feel seen and supported.
If you’re preparing for or currently in treatment, I’d love to walk with you through this season. Reach out to learn how doula support can bring balance, grounding, and hope to your IVF or TTC experience.
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