Zygote scoring system of Tesarik et al. . Zygotes showing a normal morphology are classified as “pattern 0”, and zygotes showing an abnormal morphology are classified as “non-pattern 0”. Specifically, pattern 0 include zygotes with a difference in a NPBs number between the two PN < 3, the same distribution (random or polarized) of NPBs in both PN, and at least one NPB in each PN (A and B). All the other NPBs configurations lead to classified zygotes as “non-pattern 0”.