Until relatively recently, embryo selection was done by taking into account only morphological aspects. In this case, the number of cells, the number of nuclei, whether it presented fragmentation, etc. were taken into account.
However, thanks to the revolution in the field of assisted reproduction, there are now incubators that allow us to observe the development of embryos in real time. This allows a morphokinetic study of the embryos, which improves embryo selection.