BACKGROUND: The mechanical energy of sperm is an optimal index with which to quantitatively assess the motility of sperm. The sperm energy index (SEI) is proposed as an index representing the total mechanical energy of sperm in a single field when measured using computer-assisted sperm analysis. The mechanical energy of a single sperm is given by (SEI/motile sperm count) × 100 which has been designated S-SEI. PURPOSE: The aim of the current study was to examine the relationship between SEI or S-SEI and the rate of conception in intrauterine insemination (IUI). METHOD: The materials used were 1,006 semen samples from 1,006 cycles of artificial insemination with the husband’s semen (AIH). Artificial insemination was undergone by 367 couples. The SEI and S-SEI were determined using a prepared suspension of sperm prior to IUI. RESULTS: The average rate of conception for all samples was 7.5%. The rate of conception increased as the SEI increased, and the rate of conception was consistently 9.95% at an SEI of 9.5 or higher. The rate of conception peaked at 9.7% in the range of 1.6=9.5 and 1.6<=S-SEI<2.1resulted in the highest rate of conception10%. CONCLUSIONS: A combination of the SEI and S-SEI, which are indices of the mechanical energy of sperm, could serve as a criterion to determine whether or not a couple will be able to conceive through AIH.
