2. Estradiol (E2) response to recombinant human (rh)FSH. Blood samples will be drawn through an indwelling iv catheter at 0.5-h intervals for 2 h before and at 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 16, 20, and 24 h after 150 U rhFSH injection. The E2 response to rhFSH will be assessed before and after adjusting for numbers of TVUS-detected ovarian antral follicles.