Embryo Grading Guide
Type the grade from your IVF report, like 4AB, and see what every number and letter means, with a drawing of your embryo.
- Day 5 and day 3
- Stays on your phone
- Plain answers
The day 5 grade
One number and two letters
Most labs use the Gardner scale. The number says how far the blastocyst has grown; the letters say how its two kinds of cells look.
1Early blastocyst
A small fluid-filled cavity has started to form, less than half of the embryo.
2Blastocyst
The cavity now fills half or more of the embryo.
3Full blastocyst
The cavity fills the whole embryo.
4Expanded blastocyst
The embryo has grown bigger and its shell, the zona, has thinned.
5Hatching blastocyst
The embryo has started to push out through its shell.
6Hatched blastocyst
The embryo has fully left its shell.
First letter: the inner cell massThe cluster inside that becomes the baby
- AMany cells, tightly packed
- BSeveral cells, loosely grouped
- CVery few cells
Second letter: the outer layerThe ring of cells that becomes the placenta
- AMany cells forming a smooth, even layer
- BFewer cells forming a looser layer
- CVery few, large cells
How many clinics group them
- AAExcellent
- AB, BAGood
- BB, AC, CAFair
- BC, CB, CCLower grade
Based on the Gardner blastocyst scale (Gardner and Schoolcraft, 1999). Labs differ a little in how they group grades.
Day 3 embryos
On day 3, the lab counts and looks at the cells
About 8 cells
On day 3 a healthy embryo usually has 7 to 9 cells. Fewer means slower, more means faster.
Fragmentation
Small loose pieces of cell. Under 10% is grade 1, 10 to 25% grade 2, over 25% grade 3.
Even sizes
Cells should be the size expected for their stage. Very uneven sizes lower the grade.
Based on the Istanbul consensus on embryo assessment (ESHRE and ALPHA, 2011).
Keep it in proportion
What a grade cannot tell you
A grade is a snapshot of how an embryo looks under a microscope on one day. It is useful, and it is not the whole story.
Whether the chromosomes are normal
Only genetic testing (PGT-A) can check that, and it has its own limits.
Day 5 or day 6 is not pass or fail
Day 5 blastocysts do a little better on average, but good day 6 ones give many healthy pregnancies.
Freezing does not undo a good grade
With today's fast freezing (vitrification), most good blastocysts survive thawing.
A lower grade is not a no
Grading looks at shape under a microscope. Healthy babies are born from lower grade embryos too.
Before your transfer
Six questions to ask your embryologist
They are happy to explain. Take this list with you.
- 1
What grade is each of our embryos, and on which day?
- 2
Which embryo would you transfer first, and why?
- 3
How does your grading scale compare with this one?
- 4
How many embryos are good enough to freeze?
- 5
Would genetic testing (PGT-A) help in our case?
- 6
What happens to the embryos we do not use?
Questions
What people ask about embryo grades
Every embryo is a real chance.
Our specialists can go through your embryo report with you, grade by grade, without any pressure.
What does 4AA mean?
The 4 means an expanded blastocyst. The first A means the inner cell mass, which becomes the baby, has many tightly packed cells. The second A means the outer layer, which becomes the placenta, is full and even. It is one of the highest grades.
Is a 3BB embryo good?
Yes, it is a fair, average grade. Many pregnancies come from BB embryos, and the 3 simply means it has just filled its shell. It may expand further.
Which letter matters more?
Both matter, and research is mixed on which matters more. Your embryologist looks at the whole embryo, not one letter.
Is a day 6 blastocyst worse than day 5?
On average day 5 blastocysts do a little better, but day 6 blastocysts of a good grade still give many healthy pregnancies. Some embryos simply take longer.
Can a low grade embryo become a healthy baby?
Yes. Grading looks at shape under a microscope, not at health or genes. Lower grades have a lower average chance, but healthy babies are born from them every day.
Does grading show if an embryo is genetically normal?
No. Only genetic testing (PGT-A) can check chromosomes. A top grade embryo can be abnormal, and a lower grade one can be normal.
Why does my clinic use a different system?
Labs use slightly different scales, such as numbers instead of letters, or their own words. Ask your embryologist how their scale compares with this one.
Where are my answers saved?
Only in this browser on this device. Nothing is sent to us. Use "Start again" to clear them.
Please read: a guide, not your lab report
- This guide explains common grading scales in general terms. It is not a report on your own embryos.
- Labs grade in slightly different ways, and your embryologist sees things a grade cannot show. Go by what your clinic tells you.
- A grade gives an average picture only. It cannot say whether a particular embryo will implant or become a baby.
- If you have questions about your embryos, our specialists are happy to go through them with you.