Mitochondrial Score and PGT
Mitochondria are cellular organelles responsible for generating ATP used as an energy token in cell metabolism. Recently, measuring the number of mitochondria in the embryo was introduced as a marker of embryo quality that is reported alongside chromosomal errors in PGT reports under different names, like Mitochondrial Score etc. It has no proven clinical value and can safely be ignored.
Back in 2001 we were first to present both, chromosomal and mitochondrial evaluation on the same embryo at the ASRM annual conference.
There are two parameters of mitochondria that can be measured, mass and function. What you want to know is how active are the mitochondria, or in other words, their level of function. However, the PGT report gives you information about the amount of mitochondrial DNA, which is an indirect way to measure mitochondrial mass. We observed that the function of mitochondria does NOT have any correlation with mass.
In the image below you can clearly see that mitochondria in blastomeres have the same mass (green) while the difference in mitochondrial activity between them exceeds 400%.
In other words, mitochondria may have identical mass, but a completely different activity level, which is only one truly important parameter. Yet the activity is very difficult, and frankly, unpractical to measure on a biopsy sample for many technical reasons. One of them is that activity measurement requires intact mitochondria, which is impossible to achieve in a PGT lysis buffer.
PGS report provides the indirect measurement of the mitochondrial mass because the amplification of mitochondrial DNA can be achieved concurrently with PGS at insignificant additional cost. In other words, we have a classical situation of a hummer looking for a nail.
To sum it up, since the mitochondrial score in a PGT report does not reflect the activity of mitochondria and has not been convincingly shown to improve the chance of pregnancy it has no clinical value and can safely be ignored.