During traditional embryo grading, a microscope is used to observe the embryo stage and quality at set times only. The embryo is taken out of the incubator at regular intervals after fertilisation, generally every 24 hours. The visual appearance of embryos is observed under the microscope, including the number of cells, symmetry of cells and degree of cell fragments. The repeated removal and replacement of embryo, in and out of the incubator leads to repeated change in temperature, pH, air content etc which can be detrimental to the embryos.
In EEVA, a digital time lapse camera, e, is mounted on top of each embryo, in an incubator with controlled environmentThe camera records images of each embryo, generally every 5-15 minutes. This allows the embryologist to continuously monitor the embryo development, without having to remove the embryo from the incubator at all. . EEVA allows assessing the embryos continuously, giving a lot more information, rather than a snapshot every 24 hours. It also provides the embryos the most stable environment to grow.