OG28.3 | Ovulation Induction — Summary & Reflection

KEY TAKEAWAYS

Ovulation induction is tailored to the WHO classification of anovulation. WHO Group I (hypogonadotrophic — low FSH/LH) requires exogenous gonadotrophins; WHO Group II (normogonadotrophic — predominantly PCOS) responds to oral agents; WHO Group III (hypergonadotrophic — POI) requires donor oocytes. For PCOS (WHO Group II), the evidence-based treatment ladder is: letrozole (first-line, 2.5–7.5 mg days 2–6, based on PPCOS II superiority in live birth rates and lower multiple pregnancy rates), then clomiphene citrate (second-line, 50–150 mg days 2–6, maximum 6 cycles), then metformin adjunct (especially obese/insulin-resistant), then injectable gonadotrophins (step-up protocol with mandatory USS/E2 monitoring, cycle cancellation if >3 dominant follicles or E2 >2,500 pg/mL), then laparoscopic ovarian drilling, and finally ART. OHSS is graded mild/moderate/severe and is primarily prevented by strict monitoring, low starting gonadotrophin doses, and cycle cancellation when multiple follicles develop. Multiple pregnancy is the other key risk, highest with gonadotrophins and lowest with letrozole.

REFLECT

Return to the opening case. The patient has PCOS with insulin resistance (acanthosis nigricans) and a BMI of 29. Her friend was 'given some tablets' — almost certainly clomiphene, which was the standard of care until 2014. You now know that the evidence-based first choice is letrozole. Reflect: if you prescribed clomiphene instead of letrozole, would you be following current evidence? What would you tell the patient about the off-label status of letrozole versus the evidence base? Now consider: what would happen if you triggered her ovulation in a poorly monitored gonadotrophin cycle with 4 dominant follicles? Map the OHSS cascade in your mind — VEGF → vascular leak → third-space fluid → haemoconcentration → thrombosis risk. This is why monitoring is not optional. (Kolb: Reflect on the responsibility of prescribing: evidence changes, and the 'standard' drug may no longer be the best choice.)