Intrauterine insemination timing models—LH can only take you so far

Research question: Can an optimal LH threshold algorithm accurately predict timing of ovulation for natural cycle–intrauterine insemination (NC-IUI)? Design: A retrospective cohort study (2018–2022) including 2467 natural cycles. Ovulation timing for these cycles was determined using a previously developed AI model. Two LH thresholds, low and high, were determined in the LH algorithm. Being below the low threshold meant that ovulation is likely to occur in ≥ 4 days, suggesting another daily blood test. Between the two thresholds meant that ovulation was likely in 2–3 days, suggesting IUI the next day. Above the high threshold meant that ovulation will likely occur tomorrow, suggesting performing IUI on the same day. Results: The optimal LH model with a high threshold of 40 mIU/ml and a low threshold of 11 mIU/ml succeeded in correctly predicting timing for IUI (day − 1, − 2 relative to ovulation) in 75.4% (95%CI 75.3–75.4). In 23.1% (95%CI 23.0–23.2), the algorithm predicted “error,” suggesting performing insemination when in fact it would have been performed on a non-optimal day (0 or − 3). A previously described 3-hormone-based (LH, estradiol, progesterone) AI model performed significantly better in all parameters (93.6% success rate, 4.3 “error” rate). Conclusions: An LH threshold model, representing common practice, evaluating all possible high and low LH threshold combinations, was successful in accurately scheduling timing for IUI in only 75% of cases. Integrating all three hormones as performed in the AI model may have an advantage in accurately predicting the optimal time for IUI, over the use of LH only.