EMBRYO GRADING
Day 1 Check eggs for fertilization (the presence of two pronuclei or PN's)
Day 2 Embryos at the 4-cell or more stage of development
Day 3 Embryos at the 8-cell or more stage of development
Day 4 Embryos at the compacted morula (16-32 cell) stage
Day 5 Embryos at the blastocyst stage of development
...Critical points in development are (1) fertilization, (2) 4 to 8 cell stage and (3) morula to blastocyst stage.
With regards to grading, some clinics use the reverse scale so that Grade 4 is best...you would need to check with your own clinic and some clinics don't grade at all...
Numeric grading systems for multicell embryos usually have 4 levels (this showing Grade 1 as best):
Grade 1: even cell division, no fragmentation
Grade 2: even cell division, small fragmentation
Grade 3: uneven cell division, moderate fragmentation
Grade 4: uneven cell division, excessive fragmentation
Blastocysts are graded differently with a number and two letters.
The number refers to the degree of expansion of the blastocyst (1 is the least expanded, 6 is the most expanded). The first letter (A,B, or C) refers to the quality of the inner cell mass (the part of the blastocyst that is going to be the baby) and the second letter (A, B, or C) refers to the quality of the trophectoderm (the part of the blastocyst that is going to be the placenta).
Sometimes the laboratory uses the reversed scale where a grade 4 embryo is equivalent to a grade 1 embryo on the above scale. Check with your lab
And here's some more info...
http://www.ivf-bath.co.uk/treatments/embryo_grading.htm
However, lower grades and less cells doesn't necessarily mean that won't implant, just as higher grades can't guarantee success...
This website shows pictures of the different embryos and uses the reverse grading where grade 4 is best...
http://www.advancedfertility.com/embryos.htm
Many clinics will also only freeze grade 1 embies so usually an embie with more than 2 cells. The problem is that embies are so fragile and with the thawing process they can sometimes lose cells...so if only 2 cell embie frozen then it may not survive the thaw...although some do so would also depend on whether there was any fragmentation...
Some women may only get 3 or so eggs and some may have "lower" grade embryos but still go on to get that much wanted BFP......whilst others may get lots of eggs and "high" grade embies and BFN...there really are no guarantees sadly which is why it's probably best not to dwell too much on it.
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