OBJECTIVE To examine fertilization, cleavage, and pregnancy rates (PRs) with semen samples yielding numbers of total motile sperm per swim-up ranging from < 1 to > 20 x 10(6) and to correlate the findings with changes, if any, in the sperm motion parameters. METHODS Fertilization, cleavage, and pregnancy outcomes in 439 in vitro fertilization (IVF) cycles were correlated with the total number of motile sperm per swim-up and the sperm motion parameters as determined with an automated semen analyzer. METHODS A university-based tertiary referral hospital center. METHODS Patients undergoing IVF or intrauterine insemination treatments for multiple etiologies. RESULTS Higher numbers of motile sperm per swim-up, most notably above the value of 3 x 10(6) motile sperm, were associated with improved fertilization rates and viable PRs. Sperm velocity, linearity, amplitude of lateral head displacement, and flagellar beat per cross frequency for sperm from swim-ups with poor or good pregnancy outcome, however, showed no significant differences. CONCLUSIONS As a group, semen samples that yield < or = 3 x 10(6) motile sperm per swim-up are associated with poor fertilization rates, cleavage rates, and PRs. This relationship can not be attributed to differences in sperm motion parameters.