**2.1.3 Sperm motion characteristics analysis by using CASA**

Sperm motion characteristics were assessed by using a computer-assisted sperm motion analysis system (CASAS-QH-Ш, Tsinghua Tongfang Inc., Beijing, China) at room temperature (18oC to 20oC). The method for computer-assisted sperm motion analysis was describied in Liu et al (2007b). The designation of the motility status was based on the level of the average path velocity (VAP). Sperm with average path velocity <5 μm s-1 were considered immotile, with average path velocity >20 μm s-1 were defined as motile, and 5– 20 μm s-1 as locally motile. Therefore, in the present study sperm motility includes the percentage of local motile sperm and motile sperm. Motility and velocity of fresh and postthaw sperm were quantitatively recorded by CASA immediately 10 s after activation, and changes of motility of post-thaw sperm frozen with 15% DMSO were observed every 30 s.
