Semen Parameter Criteria for IUI
While definitive lower cut-off values cannot be established with certainty, IUI should generally be considered when the total motile sperm count (TMSC) is >10 million in the ejaculate, with post-wash TMSC >1 million and sperm morphology >4% representing possible minimum thresholds below which success rates decline significantly. 1
Primary Semen Parameters
Total Motile Sperm Count (TMSC)
- TMSC >10 million in the ejaculate is recommended as the threshold for IUI with ovarian stimulation, particularly in couples with unexplained infertility or mild male factor 1
- TMSC between 3-10 million may be considered for IUI in natural cycles, though success rates are lower 1
- Post-wash TMSC thresholds vary considerably in the literature (0.8-5 million), but post-wash TMSC >1 million represents a possible minimum threshold 1
- When initial TMSC is ≥5 × 10⁶, pregnancy rates of ≥8.2% per cycle can be expected 2
Sperm Morphology
- Sperm morphology >4% normal forms is a critical threshold value below which IUI becomes significantly less effective 1
- Teratozoospermia (normal morphology <50%) significantly reduces IUI success, particularly when combined with oligozoospermia or asthenozoospermia 3
- In severe cases with both teratozoospermia and severe oligozoospermia/asthenozoospermia (motile sperm count <5 × 10⁶/mL), no pregnancies were achieved in one study 3
Sperm Motility
- Progressive motility ≥30% is associated with reasonable IUI success rates 2
- Post-wash sperm motility is a significant predictor of live birth outcomes 4
- The lowest initial motility value resulting in pregnancy was 17%, though success rates were <3.6% at such low levels 2
Clinical Decision-Making Algorithm
When to Proceed with IUI:
- TMSC >10 million + morphology >4%: IUI with ovarian stimulation is first-line treatment 1
- TMSC 3-10 million + morphology >4%: Consider IUI in natural cycles 1
- Progressive motility ≥30%: Proceed with IUI 2
When to Consider Alternative Treatments:
- TMSC <3 million or post-wash TMSC <1 million: IUI success is unlikely; consider IVF/ICSI 1
- Morphology <4% combined with severe oligozoospermia: IVF with ICSI may be more appropriate 1, 3
- Post-wash motility poor combined with advanced female age (>37.7 years) or history of pelvic surgery: No successful pregnancies achieved in one study 4
Important Caveats
Lack of Definitive Thresholds
The evidence consistently shows that it is not possible to define clear lower cut-off levels of pre- or post-wash sperm parameters below which IUI should be absolutely withheld 1. The thresholds provided represent prognostic values with poor sensitivity for predicting pregnancy but high specificity for predicting failure 1.
Sperm Concentration Considerations
- Minimum sperm concentration of ≥5 × 10⁶/mL is associated with reasonable success 2
- Total sperm count ≥10 × 10⁶ in the ejaculate correlates with better outcomes 2
- The lowest concentration resulting in pregnancy was 2 × 10⁶/mL, though success rates were very low 2
Preparation Technique
Any standard semen preparation technique (swim-up, gradient centrifugation, or wash and centrifugation) can be used, as there is insufficient evidence to recommend one method over another 1, 5
Additional Factors Affecting Success
- Female age <38 years significantly improves outcomes 6, 4
- Absence of corrective pelvic surgery history improves success rates 4
- Post-wash sperm count >1 × 10⁶/mL after conventional preparation is associated with better outcomes 6
Recommendation for Equivocal Cases
When semen parameters fall in borderline ranges (TMSC 3-10 million, morphology 4-10%, motility 20-30%), proceed with at least 3 consecutive IUI cycles before transitioning to IVF/ICSI, as pregnancy rates continue to increase through multiple cycles 1, 7. However, if no pregnancy occurs after 3 cycles with borderline parameters, strongly consider advancing to IVF with ICSI 8.