Stage 8, Hatching Blastocyst.
A. Quality 1, Excellent. The expanding blastocyst is emerging from the fractured zona pellucida. The intercell mass is well delineated as is the layer of trophoblast cells lining the zona pellucida. B. Quality 2. Fair to Good. The collapsed embryo has shed the zona pellucida. Comment about C and D: Quality 3 and 4 hatched blastocysts, i.e. poor and degenerating hatched blastocysts are rarely identified as they resemble tissue fragments and debris. Suspicious material can always be incubated and potential further development monitored.
Wright JM (2004)