Observed patterns of early embryo development: (a) normal development with division of zygote in two blastomeres in the first cell cycle (ECC1) and second embryo cell cycle (ECC2) leading to 4-cell embryo that can be observed on day 2 of cultivation. In the third embryo cell cycle (ECC3), the 4-cell embryo duplicates all blastomeres and an 8-cell embryo can be observed on day 3 of cultivation. (b–e) Cleavage irregularities: (b) direct cleavage of a cell in more than two blastomeres (in the ECC1 in the upper row and in ECC2 in the lower row) usually with tripolar cleavage furrow that leads to 3 equally sized cells. (c) Chaotic cleavage in ECC1 with no bipolar cleavage furrow observed, membrane ruffling of the zygote, and extensive fragmentation during division in two or more cells. (d) Reverse cleavage: the reduction of the number of blastomeres of an embryo due to blastomere fusion. The process can be observed at any point of development, here presented as reverse cleavage of two blastomeres into one cell. (e) Arrested development: when embryos had fewer blastomeres than expected and did not approximately double the number of cells every 24 hours.