Table 1.

Combined scoring system (CSS) of embryos

Evaluation	Time after insemination (h)	Development milestone	Score
1	16~18	Z-1 zygote	20
		Z-2 zygote	10
2	25~27	Cleavage regular and symmetrical	20
		Fragmentation*: Absent	30
		<20%	25
		>20%	0
3	64~67	Cell number and grade**: 7I; 8I; 9I; 8II; compacting I	30
		7II; 9II; 10III; 11III	15
Total score			100

^*If the embryo was not cleaved at 25~27 h, grading of fragmentation should be carried out during the 64~67 h evaluation.

^**Grade I: Symmetrical blastomeres and no fragmentation; Grade II: Slightly uneven blastomeres and <20% fragmentation; Grade III: Uneven blastomeres and >20% fragmentation