To identify predictors of pregnancy rate (PR) among women undergoing homologous IUI. Cross-sectional analysis of IUI cycles carried out from January 2000 to September 2002. Private infertility center in Alicante, Spain. Four hundred seventy women undergoing 1,010 cycles of IUI. Single IUI with ovarian stimulation using hMG. Preovulatory follicles (>15 mm), motile spermatozoa count, type and duration of infertility, female age, insemination timing, and cycle number. Overall PR per cycle and multiple pregnancy and miscarriage rates were 9.2%, 8.6%, and 11.8%, respectively. Three significant predictors of pregnancy were identified by multiple logistic regression analysis: preovulatory follicles, spermatozoa count, and infertility duration. Interuterine insemination with three follicles almost tripled the PR with respect to only one, odds ratio (OR) = 2.89 (95% confidence interval [CI], 1.54-5.41). Compared with insemination with a motile sperm count >30 x, 20.1-30, 10.1-20, 5.1-10, and < or =5 x10(6), insemination progressively decreased the PR, from 15.3% in the highest category to 3.6% in the lowest (OR lowest/highest = 0.20 [95% CI: 0.09-0.45]), with a statistically significant dose-response trend. Infertility duration > or =3 years was marginally associated with a lower PR, OR = 0.65 (95% CI, 0.40-1.04). Overall, female age was not a significant predictor of pregnancy, and although PR slightly decreased beyond two IUI cycles and when a single IUI was performed 36-40 hours after hCG administration, results were not statistically significant. Homologous IUI achieves the best results with two or three induced follicles, a high motile spermatozoa count, and infertility duration <3 years, irrespective of female age and fertility history.
