Abstract: Objective　To evaluate the sperm parameters in semen analysis and before/after preparation that can affect the clinical pregnancy rate after intrauterine insemination (IUI).　Methods　A single centre retrospective observational cohort study included 696 IUI cycles among couples in unexplained and male subfertility treated with gonadotrophins.  Results　The clinical pregnancy rate in women inseminated with 30×106/mL in the native semen was higher than those inseminated with＜15.0×106/mL or 15.0×106~29.9×106/mL (15.2% vs 6.1%, 8.3%, respectively)(P<0.05). When the motility in the native semen was 21%~30%, the clinical pregnancy rate after IUI was noted higher than those inseminated with semen motility of 11%~20% or＞30% (21.6% vs 4.2%, 12.6%, respectively)(P<0.05). The clinical pregnancy rate was influenced by total motile spermatozoa count in the native semen (TMSC) and inseminating motile count after washing (IMC), with the cut-off value of 10 million and 5 million, respectively. And 42.9% of sperm was evaluated with the same result in its morphology by 4 andrologists. There were no strong correlations between sperm parameters at the time of semen analysis and clinical pregnancy rates after IUI. By multivariate logistic regression analysis three factors were identified to be associated significantly with clinical pregnancy rate: the sperm concentration in the native semen, the number of preovulatory follicles (≥18 mm), and the endometrial thickness.　Conclusions　The concentration in the native semen is significantly associated with the clinical pregnancy rate after IUI and is an independent factor to affect IUI outcome. Various sperm parameters in semen analysis are not correlated with IUI outcome.

Key words: Sperm concentration, 　Sperm motility, 　Sperm morphology, 　Intrauterine insemination, Clinical pregnancy rate