Determinants of the outcome of intrauterine insemination: Analysis of outcomes of 9963 consecutive cycles

OBJECTIVE: Our aim was to determine which factors influence the effectivene ss of intrauterine insemination. STUDY DESIGN: This article is a retrospective statistical analysis of outco mes of 9963 consecutive intrauterine insemination cycles. RESULTS: Patient age was the main determinant of pregnancy outcome (analysi s of variance F ratio = 29, P < .0001), followed by the number of follicles at the time of intrauterine insemination (analysis of variance F ratio = 9 , P < .0001) and sperm motility in the inseminate (analysis of variance F r atio = 4, P = .002). A total of 18.9% of all patients <26 years old conceiv ed, compared with 13.9% of those 26-30 years old, 12.4% of those 31-35 year s old, 11.1% of those 36-40 years old, 4.7% of those 41-45 years old, and 0 .5% of patients >45 years old (P < .001). When analyzed by single years, on going pregnancy rates after intrauterine insemination remained high through age 32 years. Across all ages and causes of infertility, 7.6% of patients with 1 follicle at the time of intrauterine insemination conceived, compare d with 10.1% with 2, 14.0% with 4, and 16.9% with 6 follicles (P < .01). Wh en ovulation occurred before intrauterine insemination (ie, no visible foll icular structures), 4.6% of patients conceived. The likelihood of pregnancy was maximized when motile sperm numbers were greater than or equal to 4 mi llion and sperm motility was greater than or equal to 60%. Differences in p regnancy outcomes between sperm processing options were related to differen ces in sperm motility after processing; use of methods incorporating motili ty enhancement with pentoxifylline and motile sperm concentration through s ilica gradients yielded the highest overall pregnancy rates. CONCLUSION: When the results of ongoing retrospective analysis of intrauter ine insemination outcomes are applied, overall intrauterine insemination pr egnancy rates have increased from 5.8% per cycle in 1991 to 13.4% per cycle in 1996, during which time the average age of patients undergoing intraute rine insemination has increased from 36.1 (+/-0.2) to 39.2 (+/-0.1) years.