 The maximal starting dose of Letrozole will be 5 mg, regardless of the initial estradiol level. The Letrozole dose may be reduced if the appropriate suppression of estradiol occurs. The maximal increase or decrease in Letrozole dose will be 2.5 mg day. Patients will be monitored with blood tests for estradiol and LH and sonograms starting on the second day of gonadotropin stimulation and every 1-3 days to monitor response and adjust medication dose as per our usual IVF protocol. Letrozole will be stopped for both groups on the day that HCG is given and resumed after egg retrieval. All patients will stay on the same dose of Letrozole that was required for their last day of ovarian stimulation for 2 weeks after stimulation to keep estradiol levels at a minimum. In addition, patients will have serum estradiol levels drawn weekly for 2 weeks after stimulation. Follow-up vital signs will be recorded along with CBC, liver function panel, and cholesterol panel 2 weeks after stimulation. They will also be asked to return 6 months to 1 year after completion of chemotherapy for AMH and FSH levels to evaluate ovarian reserve, and then followed on a yearly basis by phonemail questionnaire or in person with an annual gynecological examination. 