Embryo Grading Generally, embryo transfer occurs either on day 3 or day 5, or frozen embryos. When the egg is first removed, it is only a single cell, which develops and divides in culture 12-24 hours after fertilization, so by the third day it is usually a 4-8 cell embryo (Embryo). By the fifth day, the embryo develops into about hundreds of cells, and at this time it is also called a blastocyst. In between (usually on the fourth day), there is another stage called morula, which is generally not graded because it is more difficult to do so. Grading of Day 3 (D3) embryos In general, embryo grading is related to several factors: the number of cells in the embryo, the uniformity of the cells after division, and the degree of fragmentation. A more common grading method is described here first, which is from grade 1 to grade 4, with grade 1 being the best and grade 4 being the worst. Embryo grade Description Grade 1: uniform cell division; no debris Grade 2: uniform cell division; some debris Grade 3: uneven cell division; no debris or some debris Grade 4: uniform or uneven cell division; more severe debris Here is a little additional information about why there is debris. Fragmentation is a sign of apoptosis. When an embryo is stressed by its own causes or by the environment in vitro, it generates DNA repair mechanisms and expels cellular components that are harmful to the organism, resulting in fragmentation. Therefore, the more fragmented an embryo is, the worse its growth potential is, and this becomes an important indicator of a good or bad embryo. Generally, the third day embryos of grade 1 and grade 2 are very good. Grade 3 are a little worse, but still usable. Grade 4 are less likely to be transferred or frozen. For example, if you are told that the third day embryo is a grade 1 8-cell, then congratulations, there is still a good chance of success. Of course, the goodness of the embryo is also related to the age of the patient. For the same level 1 8-cell, the chromosomal coefficient of variation is very low in a young woman, while the coefficient of variation is relatively much higher in an older one. Some fertility centers like to express the third day embryo rating in Roman I-IV and some like to express it in A-D. Actually, the reference descriptions are pretty much the same. An example of embryo labeling commonly used in our fertility centers: D3 8C/1, it means this is an embryo on day 3 of fertilization, dividing into a total of 8 cells and graded as grade 1. Day 5 (D5) blastocyst grading The development of blastocysts is divided into six periods based on the size of the blastocyst cavity and whether it hatches or not. Stage 1: early chambered blastocyst with blastocyst cavity less than 1/2 of total embryo volume; Stage 2: blastocyst cavity volume greater than or equal to 1/2 of total embryo volume; Stage 3: fully dilated blastocyst with blastocyst cavity completely occupying total embryo volume; Stage 4: dilated blastocyst with blastocyst cavity completely filling the embryo, total embryo volume becoming larger and zona pellucida becoming thinner; Stage 5: hatching blastocyst with part of blastocyst escaping from zona pellucida Stage 6: hatching blastocyst with all the blastocysts escaping from the zona pellucida. Some embryos develop slowly and do not develop into blastocysts until day 6 (D6) or even day 7 (D7). Therefore the number of days of blastocyst is still an important indicator of its developmental potential. Generally speaking, D5 is the best, D6 is the second best, and D7 is the second best. D7 blastocysts are a bit slower and have a lower transfer success rate, but they are still very good if they have not “died” by this time, so don’t give up lightly.