To detect equivalence of COCP to luteal estradiol with a power of 90% at an alpha of .05 assuming a 10% attrition rate, we will enroll women into each study group so as to achieve final number of 10 cycles per treatment group. We assume that an additional 50% decrease in follicular size would prove COCP superiority. To detect superiority of COCP to luteal estradiol with a power of 80% at an alpha of 0.05 assuming 10% attrition rate, we will enroll women into each study group so as to achieve a final number of 28 cycles per treatment group. Only newly initiated treatment cycles will be included; only the first cycle of patients' crossing over to the other treatment group will count toward this recruitment goal. The second cross over cycle will be compared within patient.