Introduction: Biomarkers of embryo viability: the search for the "holy grail" of embryo selection.

Overview

Over the past four decades we have witnessed great progress and increasing pregnancy success rates with in vitro fertilization. However, this apparent success has been accompanied by the burden of multiple pregnancies. While efforts to reduce the number of embryos transferred have had a salutary impact on the incidence of high order multiple pregnancies, twin gestations have not diminished significantly. Thus, the search for a marker of embryo quality with the goal of selecting the single best embryo for transfer continues to be the major challenge facing our field. The four contributions in this Views and Reviews present several contemporary approaches, both invasive and non-invasive, for evaluating embryo viability. Each group makes the case that recent techniques, including time-lapse microscopy, biomechanical markers for oocytes and embryos, novel non-invasive methods of evaluating embryo metabolism and function as well as measurement of mitochondrial DNA, will allow the identification of the single best embryo for transfer. They describe several promising markers of embryo viability, although the goal of finding the "holy grail" of embryo selection has not yet been realized.