Symposium: innovative techniques in human embryo viability assessment. Oocyte assessment and embryo viability prediction: birefringence imaging.

Embryo viability is a key element for success in assisted reproduction. Since the beginning of the era of assisted reproduction treatment, embryo viability was mostly considered to be a function of developmental progression during the preimplantation phase. In the last decade, several morphological criteria of oocytes and embryos were evaluated with regard to their potential for predicting embryo viability. The introduction of polarization light microscopy systems in assisted reproduction has enabled the detection of structures within oocytes that possess a natural birefringence. Birefringence imaging of the meiotic spindle and the zona pellucida in living animal and human oocytes represents a new approach in the assessment of oocyte and embryo viability. The technique was applied in several studies to select oocytes in order to improve treatment success. This review will summarize the present knowledge of birefringence imaging. The various applications in basic and clinical research as well as in clinical treatment will be presented, especially with regard to their effect on assisted reproduction.