Intrauterine insemination with donor sperm (IUI-D) is an assisted reproductive technology (ART) offered to couples with definitive male infertility or risk of genetic disease transmission. Here, we sought to evaluate our practice in IUI-D and identify factors that influenced the success rate. We performed a retrospective, single-center study of all IUI-D procedures performed at Lille University Medical Center (Lille, France) between January 1, 2007, and December 31, 2017. Single and multivariate analyses with a mixed logistic model were used to identify factors associated with clinical pregnancies and live births. We included 322 couples and 1179 IUI-D procedures. The clinical pregnancy rate was 23.5%, and the live birth rate was 18.9% per IUI-D. In a multivariate analysis, the women's age was negatively associated with the live birth rate. The number of motile spermatozoa inseminated was the only factor associated with both clinical pregnancies and live births, with a chosen threshold of 0.75 million. The clinical pregnancy and live birth rates were, respectively, 17.3% and 13.0% below the number of motile spermatozoa inseminated threshold and 25.9% and 21.0% at or above the threshold (all P = 0.005). The number of motile spermatozoa inseminated was the only factor that significantly influenced both pregnancies and live-birth rates after IUI-D. Indeed, below a threshold of 0.75 million motile spermatozoa inseminated, those rates were significantly lower. Application of this number of motile spermatozoa inseminated threshold may help centers to allocate donations more effectively while maintaining reasonable waiting times for patients.