Superovulation will be conducted with 100 mg of oral clomiphene citrate (Clomifene; Young Poong Pharmaceutical, Incheon, Korea) for 5 days starting on day 3 of the menstrual cycle, followed by daily injection of 150 IU of human menopausal gonadotropin (hMG;Menogon; FerringPharamceutical Co, Germany). When more than 2 dominant follicles reached a diameter of 17 mm or the urinary specimen showed positive results for luteinizing hormone (LH) surge, 5000 IU of hCG (Pregnyl; Organon, Oss, the Netherlands) was injected intramuscularly.