The fall season is upon us and with October comes crunchy leaves, cooler temperatures and the hint of frost, along with the Thanksgiving holiday.  Thanksgiving, occurring on the second Monday in October, is an annual Canadian holiday to give thanks at the close of the harvest season. What are you thankful for this year?  The BTL team would like to take this opportunity to not only give thanks to farmers for all the work and commitment put into our agriculture as well as all our clients for the friendship and opportunity to work with them. 

Morphological evaluation of embryo quality is performed for three major reasons. First reason is to differentiate between embryos and unfertilized ova. Careful evaluation of harvested embryos/ova is necessary to ensure that viable embryos are not discarded or, conversely, that unfertilized ova are not transferred or cryopreserved. The second reason to perform morphological assessment of embryos harvested from a donor is to determine if the developmental stage of the embryos is consistent with the expected developmental stage based on the days since estrus that the embryos were collected. There is often a high degree of variability in observed stage of embryonic development among embryos obtained during embryo recovery from a single donor female, and this variation in stage of development should be considered when selecting a suitable recipient female. The third reason to assess embryo quality is to enable technicians to have sufficient information on which to base the decision to transfer or to cryopreserve the harvested embryos. Poorer-quality embryos that may result in pregnancies if transferred fresh usually do not survive the cryopreservation process.

The reason for grading is to estimate the expected pregnancy rate so the embryo should be judged on its appearance and not what was expected. For instance following freezing and thawing the trophoblast layer of a blastocyst will frequently collapse leaving the appearance of a small, dark morula, therefore it should be graded as such. Obviously grading is subjective and in many cases there is very little difference between the success of embryos graded 1 or 2 especially between two operators.

This month we are pleased to share an article written by Dr. Peter Elsden that we found in our internet travels at ETschool.com, regarding bovine embryo classification and grading.

We hope you enjoyed your summer as we settle into the fall season.

~Andres, Melissa and Lisa 

Embryos Collected at Bova-Tech

Recently a cattle owner contacted Dr. Peter Elsden 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 article:

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.

Written by Dr. Peter Elsden of ETschool.com

Quality Evaluation

• Excellent: An ideal embryo, spherical, symmetrical and with cells of uniform size, color and texture.

• Good: Small imperfections such as a few extruded blastomeres, irregular shape and a few vesicles.

• Fair: Problems that are more definite are seen, including presence of extruded blastomeres, vesiculation, and a few degenerated cells.

• Poor: Severe problems, numerous extruded blastomeres, degenerated cells, cells of varying sizes, large and numerous vesicles but an apparently viable embryo mass. These are generally considered to be not of transferable quality.

   

Recommended Quality Codes [IETS Manual]

The IETS recommended codes for embryo quality range from "1" to "4" as follows:

• Code 1: Excellent or good. Symmetrical and spherical embryo mass with individual blastomeres (cells) that are uniform in size, color and density. This embryo is consistent with its expected stage of development. Irregularities are relatively minor and at least 85% of the cellular material is an intact, viable embryo mass. This judgment should be based on the percentage of embryo cells represented by the extruded material in the perivitelline space. The zona pellucida should be smooth and have no concave or flat surfaces that might cause the embryo to adhere to a Petri dish or a straw.

• Code 2: Fair. Moderate irregularities in overall shape of the embryo mass or size, color and density of individual cells. At least 50% of the cellular material is an intact, viable embryo mass.

• Code 3: Poor. Major irregularities in shape of the embryo mass or size, color and density of individual cells. At least 25% of the cellular material is an intact, viable embryo mass.

• Code 4: Dead or degenerating. Degenerated embryos, oocytes or 1-cell embryos; non-viable.

Should you have any questions regarding embryo classification and grading we are always happy to chat with you.

Wishing you a very happy thanksgiving holiday!