Context: Body mass index (BMI) reflects the amount of insulin in the human follicle and may enhance insulin action as a cogonadotropin.

Objective: This study examines whether increased adiposity enhances intrafollicular steroidogenesis in normoandrogenic ovulatory women receiving GnRH analog/recombinant human (rh) FSH therapy for in vitro fertilization (IVF).

Design, Setting and Participants: Study participants were from an institutional practice and comprised 30 normoandrogenic ovulatory women who were lean (N=17; BMI <25 kg/m²) or overweight (N=13; BMI 25 kg/m²). Women received GnRH analog after basal serum hormone determinations and oral glucose tolerance testing, followed by rhFSH therapy and human chorionic gonadotropin administration when 2 follicles 18mm in diameter were present.

Intervention: Follicle fluid (FF) was aspirated at oocyte retrieval from the first follicle of each ovary.

Main Outcome Measures: FF was assayed for estradiol (E₂), progesterone (P₄), 17-hydroxyprogesterone (17OHP₄), androstenedione (A₄), testosterone (T), dihydrotestosterone (DHT), insulin, glucose and lactate.

Results: Overweight women had hyperinsulinemia (P=0.03) with decreased serum sex hormone binding globulin (P=0.001) and increased serum free T levels (P=0.02). Elevated intrafollicular insulin levels in overweight women (P=0.004) were accompanied by normal glucose and lactate levels. Intrafollicular E₂ levels were greater in overweight versus lean women (P=0.03), while the remaining intrafollicular steroid levels were similar in both female groups.

Conclusion: In normoandrogenic ovulatory women undergoing IVF, increased adiposity elevates insulin and E₂ levels in terminally differentiated follicles without altering intrafollicular androgen levels or luteinization. Additional studies are required to determine whether these abnormalities impair oocyte development.