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

Abstract

Objective: Our aim was to determine which factors influence the effectiveness of intrauterine insemination.

Study design: This article is a retrospective statistical analysis of outcomes of 9963 consecutive intrauterine insemination cycles.

Results: Patient age was the main determinant of pregnancy outcome (analysis 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 ratio = 4, P =.002). A total of 18.9% of all patients <26 years old conceived, compared with 13.9% of those 26-30 years old, 12.4% of those 31-35 years 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, ongoing 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, compared with 10. 1% with 2, 14.0% with 4, and 16.9% with 6 follicles (P <.01). When ovulation occurred before intrauterine insemination (ie, no visible follicular structures), 4.6% of patients conceived. The likelihood of pregnancy was maximized when motile sperm numbers were >/=4 million and sperm motility was >/=60%. Differences in pregnancy outcomes between sperm processing options were related to differences in sperm motility after processing; use of methods incorporating motility enhancement with pentoxifylline and motile sperm concentration through silica gradients yielded the highest overall pregnancy rates.

Conclusion: When the results of ongoing retrospective analysis of intrauterine insemination outcomes are applied, overall intrauterine insemination pregnancy 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 intrauterine insemination has increased from 36.1 (+/-0.2) to 39.2 (+/-0.1) years.