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Oocyte/Egg: female gamete cell provided by the ovary.
The following egg stages, we cannot perform ICSI or cryopreserve them and they will be discarded.
DAY 1 = Zygote stage
The following eggs/embryo stages are not optimal to see during the fertilization check. However, we keep them in culture to monitor future cell division and see if they reach the blastocyst stage. It is highly recommended to perform PGT-a testing on these embryos to confirm their euploidy, as we could not observe normal fertilization of the 2PN.
The following eggs or embryos are discarded because they are not compatible with life if fertilized or due to degradation.
The ideal stage for day five is to have the blastocyst or at least the early stages of it. Between 45-55% of the embryos that showed a 2PN fertilization on day one reach the blastocyst stage. This stage can be reached between days five, six, or day seven.
The earlier an embryo reaches the blastocyst stage, its chances of successful implantation are higher. However, the blastocyst grade and euploidy also influence the implantation rate. For instance, a blastocyst on day 5 has a better implantation rate than one on day 6, which is better than one on day 7. It is crucial to consider these factors when evaluating the likelihood of successful implantation.
Embryos with good prognosis on Day 5:
If the blastocyst is grade 3-4-5-6 and meets our grade standards, we will perform a biopsy and cryopreserve it. The definitions of grades A, B, and C are at this glossary’s end.
The following embryo stages with poor prognosis will be kept in culture if observed on day five but discarded if observed on day six or day seven.
The following stages will be discarded on day five and day six.
Embryos that remain in culture should exhibit signs of cellular division. The likelihood of reaching the blastocyst stage decreases if they remain in the same stage. The optimal stage for this day is a blastocyst graded 3-4-5-6. The embryos in the cleavage stage, as well as degenerated embryos, will be discarded.
If embryos do not reach the blastocyst stage, they are discarded because IVF culture media can only support them until this point.
The grade defines the progression of the blastocyst and the quantity and quality of the cells within it.
There are two types of cells in the blastocyst. One cell type forms the Inner Cell Mass (ICM). These cells will eventually grow into the fetus. The second cell type is the Trophectoderm Epithelium (TE), these cells will go on to make the placenta and surrounding structures.
PROGRESSION: Higher number means more advanced stage of the blastocyst.
Stages 1 and 2 will be reported in our laboratory as Early Blastocyst. We cannot biopsy embryos at this early stage.
Stage 3 Full Blastocyst: This type of blastocyst commonly fills more than 50 % of the blastocoel with fluid, and the ICM and TE are well differentiated. The Zona pellucida (ZP) is still a bit thick. Embryo biopsy could be performed depending on the cell junctions the embryos show.
Stage 4 Expanded Blastocyst: Blastocysts in which the blastocyst cavity is now greater than the original volume of the embryo and the ZP is thinned.
Stage 5 Hatching Blastocyst: Blastocysts or hatching blastocysts in which the blastocoel cavity is greater than the original volume of the embryo and the TE is herniating through a natural breach in the ZP
Stage 6 Completely Hatched Blastocyst: Blastocysts or hatched blastocysts are those in which the blastocyst has completely escaped from a natural breach in the ZP.
The ICM and TE are visible from grade 3 to grade 6 blastocysts, the following classification you can find in the report with the Letters: A, B, or C, (i.e., Blastocyst 3AA, the number denotes the cavity expansion grade, the first A will denote the ICM quality and the second A will classify the TE quality).
The ICM and TE are visible from grade 3 to grade 6 blastocysts, the following classification you can find in the report with the Letters: A, B, or C, (i.e., Blastocyst 3AA, the number denotes the cavity expansion grade, the first A will denote the ICM quality and the second A will classify the TE quality).
ICM
TE
References
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