Mitochondrial DNA copy number as a predictor of embryo viability.

The evaluation of embryo viability is typically based on morphologic and morphometric grading systems, which are known to be heavily affected by differences in subjective judgement. A significant proportion of euploid embryos do not implant even when the endometrium is normal, despite the wide incorporation of preimplantation genetic testing for aneuploidy. The need to improve reproductive outcomes following assisted reproductive treatments is culminating in the emergence of new research and technology with the potential to enhance embryo selection. The assessment of mitochondrial DNA content as a predictor of embryo viability has gained increasing attention among numerous promising approaches. As is common with new tools, this attention has led to both inflated expectations and serious disillusionment. Here we gather evidence to establish the true clinical applicability of this method. Controversy continues to surround this topic, adding both interest and confusion.