BACKGROUND: Embryo incubation and assessment is a vital step in assisted reproductive technology (ART). Traditionally, embryo assessment has been achieved by removing embryos from a conventional incubator daily for assessment of quality by an embryologist, under a light microscope. Over recent years time-lapse systems (TLSs) have been developed which can take digital images of embryos at frequent time intervals. This allows embryologists, with or without the assistance of computer algorithms, to assess the quality of the embryos without physically removing them from the incubator.The potential advantages of a TLS include the ability to maintain a stable culture environment, therefore limiting the exposure of embryos to changes in gas composition, temperature and movement. Additionally a TLS has the potential advantage of improving embryo selection for ART treatment by utilising additional information gained through monitoring embryo development.