Aromatase inhibition reduces the dose of gonadotropin required for controlled ovarian hyperstimulation

Objective: to compare the use of the aromatose inhibitor, letrozole, in conjunction with the follicle-stimulating hormone (FSH) injection, and FSH alone for conbtrolled overian hypertstimulation (COH) in patients with polycystic overian syndrome (PSCOS) or ovulatory infertility. Methods: This nonrandomizing study included two study groups: 26 patients with PCOS and 63 with ovulatory infertility (unexplained infertility [41 patients], male factor infertility [17 patients], and endometrosis [5 patients]), who recieved letrozole in addition to FSH; and two control groups: 46 PCOS patients and 308 with ovulatory infertility (unexplained infertility [250 patients], male factor infertility [42 patients], and endometrosis [16 patients], who recieved FSH only. All patients had intrauterine insemination (IUI). Main outcome measures included dose of FSH used per cycle, number of preovulatory, follicles greater than 16mm in diameter, cancellation rate, and pregnancy rate. Results: The fish dose required for ovarian stimulation was significantly lower when letrozole was used in both study groups compared to the control groups without a significant difference in number of follicles greater than 16 mm. IUI cancellation rate was significantly lower with letrozole treatment in PCOS patients. In women with PCOS, clinical pregnancy rate per completed IUI cycle was 26.5% in the letrozole plus FSH group versus 18.5% in the FSH-only groups. Inovulatory infertility patients, the pregnancy rate was similar in both study and control groups (11%). Conclusion: We believe that inhibition of estrogen synthesisby aromatose inhibition will release the estrogenic negative feedback, resulting in an increase in endogenous FSH secretion. Moreover, by inhibiting conversion of androgens into estrogens, accumulating androgens may increase follicular sensitivity to FSH. Such a protocol has the potential to lower Fsh treatment cost and may improve response for low responders who require high FSH doses during ovarian stimulation. Copyright (C) 2004 by the society for Gynecologic Investigation.