63 IUI success and prognosis of natural conception 4 Main results and the role of chance Data from 975 couples were available. There were 587 couples who received at least one IUI-OS cycle within 18 months after HSG of whom 221 conceived leading to an ongoing pregnancy (rate: 0.74 per couple per year over a median follow-up for IUI of 5 months). The median period between HSG and starting IUI-OS was 4 months. Out of 388 untreated couples, 299 conceived naturally (rate: 0.56 per couple per year over a median follow-up of 4 months). After creating our mimicked trial datasets, starting IUI-OS was associated with a higher chance of ongoing pregnancy by a pooled, overall hazard ratio of 1.50 (95% CI: 1.19–1.89) compared to expectant management. We did not find strong evidence that the effect of treatment was modified by a couple’s prognosis of achieving natural conception (Akaike’s Information Criterion (AIC) decreased by 1 point). The effect of treatment was dependent on when couples started IUI-OS (AIC decreased by more than 2 points). The patterns of estimated absolute chances over time for couples with increasingly better prognoses were different from the previous study but the finding that starting later yields a larger benefit of treatment was similar. We found IUI-OS increased the absolute chance of pregnancy by at least 5% compared to expectant management. The absolute chance of pregnancy after IUI-OS seems less variable between couples and starting times of treatment than the absolute chance after expectant management. Limitations, reasons for caution This is a secondary analysis, as the H2Oil trial was not designed with this research question in mind. Owing to sample size restrictions, it remained difficult to distinguish between the ranges of prognoses in which true benefit was found. Wider implications of findings We replicated the finding that starting IUI-OS later after diagnosis yields a larger absolute and relative benefit of treatment. We did not replicate the dependency of the effect of IUI-OS on the prognosis of natural conception and could not identify clear thresholds for the prognosis of natural conception when IUI-OS was and/or was not effective. Because many of these couples still have good chances of natural conception at the time of diagnosis, we suggest clinicians should advise couples to delay the start of IUI-OS for several months to avoid unnecessary treatment.
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