Clarifying the relationship between total motile sperm counts and intrauterine insemination pregnancy rates

To study the relationship between postwash total motile sperm count (TMSC) and intrauterine insemination (IUI) outcomes.

Retrospective review SETTING: Large fertility clinic PATIENT(S): A total of 92,471 insemination cycles from 37,553 patients were included in this study.

All stimulated clomiphene citrate, letrozole, and/or injectable gonadotropin IUI cycles performed at a single institution from 2002 through 2018 were reviewed. Generalized estimating equations (GEE) analysis was used to account for multiple cycles by individual patients and to adjust for female partner age, body mass index, and stimulation protocol.

Successful clinical pregnancy was defined as ultrasound confirmation of an intrauterine gestational sac with fetal cardiac activity.

A total of 92,471 insemination cycles were available to evaluate the relationship between postwash TMSC and clinical pregnancy. Pregnancy rates were highest with TMSC of ≥9 × 10⁶ and declined gradually as TMSC decreased. Complete data for the adjusted GEE analysis were available for 62,758 cycles. Adjusted GEE analysis among cycles with TMSC of ≥9 × 10⁶ (n = 46,557) confirmed that TMSC in this range was unrelated to pregnancy. Conversely, TMSC was highly predictive of pregnancy (Wald χ² = 39.85) in adjusted GEE analysis among cycles with TMSC of <9 × 10⁶ (n = 16,201), with a statistically significant decline.

IUI pregnancy is optimized with TMSC of ≥9 × 10⁶, below which the rates gradually decline. Although rare, pregnancies were achieved with TMSC of <0.25 × 10⁶. Since the decline in pregnancy is gradual and continuous, there is no specific threshold above which IUI should be recommended. Rather, these more specific quantitative predictions can be used to provide personalized counseling and guide clinical decision making.