How is an embryo chosen for IVF (embryo grading)?

An embryo starts as a single cell and then divides continually. Usually at day four an embryo has eight cells; the embryo will be graded from 1-4 (4 is the best) based on how evenly the cells have divided and how many fragments are left behind (less is better). Both of these indicators are helpful in judging which embryo has the highest chance of implanting into your uterus.