EMBRYO CLASSIFICATION AND GRADING

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Peter Elsden

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Oct 2, 2011
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36
Recently a cattle owner contacted me regarding frozen embryo classification. He had some frozen embryos stored, classified as Stage 4 which are embryos developed to the compact morula stage usually observed 6 days after first observed standing heat (estrus ) . He had been informed by several contacts that he should discard these Stage 4 embryos, which would have been a significant number as they had been stored over the years, but fortunately he did not discard them. This alarming misinformation had come from several informants and subsequently stimulated the following post:

The International Embryo Transfer Society in the early 1980s promoted and encouraged embryo transfer practitioners to grade embryos with guidelines into 4 groups. The number 1’s would be called excellent, the number 2’s called good, the number 3’s would be fair and the number 4’s are dead or degenerated.

Each of these grades are applied to the stages of embryo development.  For example compact morulae (morulas) found on Day 6 are designated as a 4, early blastocysts the next stage of development are designated as a 5, early blastocysts are a 6, and expanded blastocysts are designated as a 7. There of course is some overlapping in these stages, for example frequently one observes compact morulae also on Day 7. So you may see on a certificate an embryo and classification described as 4-1 which means it is a compact morula graded as a 1 with an excellent chance of becoming a pregnancy.

In most cases when an embryo has attained the blastocyst stage it is a number 1, so I often advise my students to flush their donors on Day 7.5 when most of the embryos will be blastocysts and easy to recognize.

Classification of embryos is far from an exact science.  For example one practitioner will diagnose an embryo as a 1 while a second practitioner will call it a 2.  Recently in a published paper there were no differences in pregnancy rates between embryos designated as 1’s or 2’s by two different practitioners. A number of years ago we were discussing how to grade embryos following freezing and thawing. Embryos prior to thawing classified as a 1 often show some damage so I grade them as a 2 or even a 3.
However, some claim that freezing damage should be ignored leaving the original grade.  This opinion obviously defeats the purpose of grading, which is an attempt to predict the coming pregnancy chances which will be lower due to freezing damage.

Remember the next time you transfer some embryos, pregnancy rates depend on the quality of the embryos before freezing, the ability of the person freezing the embryos, the storage practices, the quality and preparation of the recipients, and the skill of the person performing the transfers. So if you experience unacceptable pregnancy rates don’t forget it may not be the fault of the practitioner transferring the embryos who usually receives the blame.

Be careful where you obtain your advice on embryo transfer I have observed several incorrect pieces of advice over the internet.

May all your embryos be number 1’s, and your transfer techniques excellent.

Dr. Peter Elsden
www.ETschool.com
 

Bradenh

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Jan 10, 2010
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2,646
Location
Central Texas
Thanks Dr. Elsden for the always informational and educational posts regarding embryo work!

Glad that Individual had asked you before he acted on previous suggestions concerning his embryos
 

Bulldaddy

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Oct 5, 2009
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1,131
Location
Valley Mills, Texas
I have my embryologist put the grade 3 eggs (if any) in fresh and freeze the 1s and 2s and toss the degenerates.  Always too many eggs and not enough recips at my place so it makes sense to sort for quality.  Dr. Elsden, are you saying that grade 4 embryos are worth transferring? 
 

Peter Elsden

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Oct 2, 2011
Messages
36
I would only transfer a grade 4 embryo if there were extra recipients to spare. I once transferred a 3- embryo from a single embryo collection from a very famous holstein cow. it became a pregnancy,a bull calf was born and at 6 months of age it was sold for $131,000 !  There was a picture of the calf in Hoard,s Dairyman ( September 10,  2008 ). I originally informed the owner I was going to discard the embryo--imagine the look of horror on his face !
 

Charguy

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May 11, 2011
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68
Interesting information Dr. Elsden. I flushed a cow recently in the US and she produced 9 #1 - code stage 4 and 5 embryos for export to Canada. Yet on the recovery form there were 14 #1 embryos listed. When I enquired I was told that the 5 embryos were #1 code 4 but had extruded blastomeres and did not qualify for export. The ET tech up here said that was a minor issue and all 14 should have been washed and sent up to us. From my understanding there is little difference in pregnancy results with these types of embryos. Just wondered what your thoughts were. Im a little put off by this but if there is a valid reason for excluding the 5 embryos, I would like to know about it. Thanks for the help!
 

Peter Elsden

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Oct 2, 2011
Messages
36
Yes, I would agree with you. Providing the embryo itself grades 1 or 2 a few dead extruded cells do not effect subsequent pregnancy rates. When extruded cells are present I will usually grade the embryo as a 2 as it is smaller than usual. Extruded cells do not make the embryo illegible for export.
 

Charguy

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May 11, 2011
Messages
68
Thanks for the information. What is done is done. The tech did not wash the 5 eggs for export so I guess the ones he excluded will stay in the US. Just seems odd. At least we got 9 and hopefully we can get some good unique calves in the near future up here. Thanks again
 
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