Metabolomics: approaches to assessing oocyte and embryo quality.

Morphological evaluation remains the primary method of embryo assessment during IVF cycles, but its modest predictive power and inherent inter- and intra-observer variability limits its value. Low-molecular weight metabolites represent the end products of cell regulatory processes and therefore reveal the response of biological systems to a variety of genetic, nutrient or environmental influences. It follows that the non-invasive quantification of oocyte and embryo metabolism, from the analyses of follicular fluid or culture media, may be a useful predictor of pregnancy outcome following embryo transfer, a potential supported by recent clinical studies working with specific classes of metabolites such as glycolytic intermediates and amino acids. Such selective approaches, however, whilst adhering closely to known cellular processes, may fail to harness the full potential of contemporary metabolomic methodologies, which can measure a wider spectrum of metabolites. However, an important technical drawback with many existing methodologies is the limited number of metabolites that can be determined by a single analytical platform. Vibrational spectroscopy methodologies such as Fourier transform infrared and near infrared spectroscopy may overcome these limitations by generating unique spectral signatures of functional groups and bonds, but their application in embryo quality assessment remains to be fully validated. Ultimately, a combination of evaluation criteria that include morphometry with metabolomics may provide the best predictive assessment of embryo viability.