Evaluation of in vitro produced bovine embryos

Tags: No Tags
Comments: Comments Off
Published on: April 21, 2023

Jennifer Barfield (Colorado State University, Fort Collins, CO)
Daniela Demetrio (RuAnn Genetics, Caruthers, CA)

Stage of Development and Associated Features

Stage 4 – Morula – Blastomeres are compacted so that they cannot be fully resolved or counted. Peri vitelline (PV) space around the embryo proper is visible and the thickness of the zona pellucida (ZP) remains unchanged from
earlier cleavage stages.
Stage 5 – Early blastocyst – A small blastocoele cavity is visible and occupies less than half of the volume of the embryo proper. In most cases, the PV space remains around the embryo proper, which may or may not touch the ZP.
Stage 6 – Blastocyst – The blastocoele cavity occupies at least half of the volume of the embryo proper. Small amounts of PV space may remain or the PV space may be completely occupied by the embryo proper owing to the filling out
of the blastocoele cavity. The thickness of the ZP remains unchanged from earlier stages of development.
Stage 7 – Expanded blastocyst – The embryo proper occupies the space under the zona pellucida fully and no PV space remains. The volume of the blastocoele cavity should be larger than the inner cell mass (ICM), which should be compact and identifiable. The ZP is thinner than earlier stages of development. Expanded blastocysts may vary in diameter depending on expansion of the blastocoele cavity. Any embryo that has initiated the expansion process and is observed to have a thinning ZP may be considered stage 7. If the blastocoele cavity is collapsed, the thickness of the ZP and overall diameter of the embryo including the ZP should be used as the primary indicator of stage.
Stage 8 – Hatching blastocyst – The ZP has thinned and been breached. The trophectoderm (TE) may or may not be herniating through the opening. The ICM has further compacted and is easily identifiable. Regardless of progression of herniation (including no herniation), all embryos with an opening in the ZP (crack) in which the embryo proper is still in contact with the ZP is considered hatching. Some fresh IVP embryos have been observed to hatch without thinning of the ZP. This may be due to zona hardening or from damage sustained during handling. Embryos with a breached ZP are not suitable for export. This information should be noted on the ABC and D forms.
Stage 9 – Hatched blastocyst – The blastocyst has emerged from the ZP completely. The TE will appear bumpy without the presence of ZP. The ICM is compact and easy to identify. Embryos without a ZP are not suitable for export unless accepted by the importing country. This information should be noted on the ABC and D forms.

Morphological Quality Evaluation

Code 1 – Excellent or good – No major abnormalities in the embryo should be observed. The embryo should be symmetrical and spherical with blastomeres that are uniform in size, color, and density. In accordance with evaluations for IVD embryos, at least 85% of the cellular material contained within the ZP should be part of the embryo proper or viable embryonic mass, based on the percentage of material in the PV space relative to the embryo proper. For embryos at the early blastocyst stage of development and beyond, the ICM and TE should be easily discernable. TE cells should be even in size and light in color. The ICM should be increasingly compact as embryo development progresses. Embryos with minor deformities of the ZP that have no other deficiencies may be classified as grade 1.
Code 2 – Fair – Moderate irregularities in overall shape of the embryonic mass or in size, color, and density of individual cells. At least 50% of the cellular material should be part of an intact, viable embryonic mass. Morula with poor compaction on all or part of the embryo proper should be downgraded to a 2. Minor defects of the ICM or TE may be acceptable, but not in both. Defects of the ICM may include poor organization, poor compaction, or speckled/dense appearance of individual cells. Defects of the TE may include cells of uneven size, grouped or scattered excessively dense cells, or irregularities in the shape of the blastocoele cavity.
Code 3 – Poor – Major irregularities in shape of the embryonic mass or in size, color, and density of individual cells are observed. At least 25% of the cellular material should be part of the intact, viable embryonic mass. Major defects in both the ICM and TE are observed. Poor quality embryos may be lacking an easily discernable ICM or have very few cells of varying densities that compose a poorly organized ICM. The TE may have few cells with many tending to be larger than normal.
Code 4 – Degenerated – Unfertilized ova and embryos that have stopped developing at cleavage stages are considered non-viable if evaluations are being done 7 days after in vitro fertilization. Blastomeres may appear

IETS Guidelines – October 2022

Comments are closed.

Welcome , today is Tuesday, May 30, 2023