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The introduction of time-lapse imaging to clinical in vitro fertilization practice enabled the undisturbed monitoring of embryos throughout the entire culture period. Initially, the main objective was to achieve a better embryo development. However, this technology also provided an insight into the novel concept of morphokinetics, parameters regarding embryo cell dynamics. The vast amount of data obtained defined the optimal ranges in the cell-cycle lengths at different stages of embryo development. This added valuable information to embryo assessment prior to transfer. Kinetic markers became part of embryo evaluation strategies with the potential to increase the chances of clinical success. However, none of them has been established as an international standard. The present work aims at describing new approaches into time-lapse: progress to date, challenges, and possible future directions.

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Objective: To develop a noninvasive embryo selection algorithm consisting of time-lapse morphokinetics and the oxidative status of the spent embryo culture medium determined using the Thermochemiluminescence (TCL) Analyzer. Design: Retrospective cohort. Setting: Not applicable. Patient(s): From women participating in the oocyte donation program, data from 505 samples of spent embryo culture media samples from 292 intracytoplasmic sperm injection cycles. Intervention(s): None. Main Outcome Measure(s): Morphokinetic parameters assessed during incubation in the time-lapse system Embryoscope. Oxidative parameters (H1 sm , H2 sm , and H3 sm ) from the spent culture medium on day 5 of incubation measured using the TCL assay; and a combined assessment algorithm, including morphology, morphokinetics, and the embryo's culture medium oxidative status, developed as a tool for embryo selection, based on implantation success and confirmed ongoing pregnancy. Result(s): The levels of the oxidative parameters H1 sm , H2 sm , and H3 sm on day 5 of incubation were statistically significantly higher in transferred and vitrified embryos compared with discarded embryos and in successfully implanted embryos compared with those that did not result in pregnancy. The assessment algorithm resulted in a hierarchical classification with six embryo quality categories (A to F), associated with implantation rates of between 76.5% and 29.2%. Conclusion(s):An assessment algorithm combining morphology, morphokinetics and the embryo's culture medium oxidative status may help to improve current embryo selection methods criteria and in vitro fertilization success. (Fertil Steril Ò 2019;111:918-27. Ó2019 by American Society for Reproductive Medicine.) El resumen está disponible en Español al final del artículo.