IUI Deep Dive — Stimulation Choices, Timing, and Decision-Making

Letrozole (aromatase inhibitor) is increasingly the first-line oral agent — equal or superior to clomiphene in many populations including PCOS, with thinner endometrium and OHSS less likely.

Clomiphene citrate remains widely used and effective, though its anti-oestrogenic endometrial effect can be a drawback in some cycles.

Low-dose injectable gonadotrophins (FSH ± LH) achieve more predictable mono- or bi-follicular development but require closer monitoring and carry higher cost and multiple pregnancy risk.

Baseline scan on day 2-3 confirms no residual cyst. Stimulation begins, and follow-up scans starting around day 8 track follicle growth at 1.5–2 mm per day and endometrial thickness.

Trigger when one to three lead follicles reach 17–20 mm and endometrium is at least 7 mm with trilaminar appearance. IUI is timed 24–36 hours post-trigger for hCG, or scheduled around natural LH surge if using GnRH agonist trigger.

We cancel and convert to a different approach when:

• Four or more mature follicles develop — multiple pregnancy risk too high for IUI
• Inadequate endometrial response despite optimisation
• Premature ovulation before adequate follicle development
• Significant ovarian hyperstimulation risk on monitoring

Cancellation is a clinical decision, not a failure — the alternative is exposing the patient to triplet pregnancy or worse outcomes.

The clinical decision to move to IVF should be triggered by:

• Three failed appropriately-timed and adequately stimulated IUI cycles
• Reduced ovarian reserve discovered during monitoring (AMH below 1.2 ng/ml)
• Newly identified tubal pathology on monitoring scans
• Worsening male factor on repeat semen analysis
• Age advancing past 35 with continued unsuccessful cycles