PURPOSE: To determine intrafollicular concentrations of letrozole (LTZ) and key steroids in women undergoing ovarian stimulation (OS) with or without LTZ co-treatment, and to explore associated clinical outcomes. METHODS: Follicular fluid (FF) collected at oocyte pickup from 30 women participating in the RIOT-B study, a randomized controlled trial comparing OS with recombinant FSH (150 IU/day) combined with either LTZ (5 mg/day; n = 15) or placebo (n = 15). Concentrations of LTZ and steroid were quantified by LC-MS/MS. Associations between FF composition and clinical outcomes were evaluated. RESULTS: levels remained unchanged. Among LTZ-treated women, higher FF concentrations of LTZ and testosterone were significantly associated with failure to conceive. No relationship was observed between FF LTZ levels and BMI or gonadotropin dose. CONCLUSIONS: . These findings suggest complex, cell-specific effects of aromatase inhibition on follicular steroidogenesis and raise questions regarding the optimal dosing and mechanistic rationale for LTZ co-treatment in assisted reproduction.
Elfrink et al. (Mon,) studied this question.