Fig. 1

Treatment protocol of ovarian stimulation. On the menstrual cycle day 2, 3 or 4, ovarian stimulation was started with a single injection of corifollitropin alfa (Elonva®; MSD), of which the dosage was determined by the patient’s body weight (150 μg for > 60 kg and 100 μg for ≦ 60 kg). Medroxyprogesterone acetate (MPA) (Provera® 5 mg/tablet; Pfizer) 5 mg twice a day was initiated orally from the day after Elonva injection. Seven days after Elonva injection, follicle development was monitored by transvaginal sonography as well as serum hormone levels of E2, LH and P. The patients received trigger at night if at least three leading follicles reached above 17 mm in diameter, and the final tablet of MPA was taken in the morning of the trigger day. If the folliculogenesis was insufficient for trigger, additional HMG (Menopur®, Ferring) 150 ~ 225 IU/day would be administered for days until the requirement for trigger was met