Time-lapse monitoring as a tool for clinical embryo assessment

As elective transfer of a single embryo (eSET) becomes increasingly accepted, the need to improve implantation rates becomes crucial. Selecting the most competent embryo therefore constitutes a major challenge in assisted reproductive technology. Embryo morphology and developmental stage at given time points are closely correlated with developmental competence and assessment of morphological parameters at discrete inspection points thus remains the preferred way of evaluating embryonic potential. Lately, more attention has been given to the assessment of dynamic embryo development as a tool for evaluating embryonic potential. The introduction of time-lapse equipment approved for use on human embryos offers novel clinical opportunities for continuous monitoring of embryos, enabling flexible evaluation of known morphological parameters and potentially introducing new dynamic markers of viability. Due to lack of larger, randomized clinical studies it remains to be elucidated whether embryo selection using dynamic parameters improves clinical outcome and which parameters are of significance. Before such randomized controlled studies are organized, the most promising parameters to evaluate must be identified. This mini-review summarizes the current knowledge about dynamic markers of viability and discusses the potential clinical role of time-lapse analysis in embryo assessment and selection.