Optimizing outcomes in intrauterine insemination: A narrative synthesis of two decades of clinical research (2000-2024).

Intrauterine insemination (IUI) is a widely used first-line fertility treatment, yet its success rates vary considerably. This review synthesizes evidence from peer-reviewed studies published between 2000 and 2024, including randomized controlled trials, cohort and case-control studies, as well as systematic and narrative reviews identified through structured searches of PubMed and Google Scholar, to examine the influence of patient characteristics, procedural variables, and environmental factors on IUI outcomes. Maternal age, body mass index (BMI), psychological stress, and nutritional status (insufficient intake of unsaturated fatty acids, vitamins [folate, B12, A, C, and E], minerals [nickel, zinc, and selenium]), strongly influence treatment success. Female-specific factors, including the number of mature follicles, endometrial thickness (6-10 mm), and ovarian stimulation protocols are consistently associated with improved pregnancy rates. Male-related determinants such as total motile sperm count, morphology, and DNA fragmentation index also play a significant role in influencing outcomes. In addition, procedural interventions, including slow-release insemination, use of soft catheters, and luteal phase support, have demonstrated potential benefit in some studies; however, the evidence is drawn from small RCTs and observational studies, with heterogeneous effect sizes, and therefore findings should be interpreted cautiously. Environmental exposures, including tobacco, alcohol, and reproductive toxins, further modulate IUI efficacy, especially when combined with modifiable lifestyle factors. This narrative review highlights that IUI success is strongly influenced by specific clinical thresholds and patient characteristics. Higher pregnancy rates are observed when endometrial thickness is within 6-10 mm, post-wash total motile sperm count is ≥5-10 million, and gonadotropin-based stimulation protocols are used. Additionally, maintaining a healthy BMI, ensuring adequate micronutrient intake, and avoiding tobacco and alcohol exposure appear to support more favorable outcomes. These findings emphasize the importance of integrating evidence-based clinical criteria with modifiable lifestyle optimization when selecting and managing IUI candidates.