Embryo Grading
Embryo grading is an attempt to evaluate abnormalities of individual embryos as they relate to the potential of establishing a pregnancy after transfer. They are graded one through four, with Grade 1 being normal and Grade 4 being severely damaged or degenerated.
Abnormalities in the distribution of fluid are common, and leaks involving the capsule are considered more important than those from the blastocoele.
Unfortunately, grading can only evaluate normal versus abnormal morphology and can in no way evaluate the health of the visible cells. An embryo can have a large number of dead cells and still appear structurally normal until growth or deterioration take place.
Cells that have been dead or stressed for some time will appear darker and are often extruded from the embryo. These are generally visible in the early blastocyst or morula, beneath the zona pellucida.