All patients in the initial cohort were treated with long protocol for ovarian stimulation. For pituitary down-regulation, patients were treated with daily administration of 0.5 mg buserelin (suprefact, Aventis, Frankfurt, Germany) from day 21 of menstrual cycle. Buserelin was reduced to 0.25 mg daily when ovaries were quiescent on ultrasound, and COH was initiated with recombinant FSH (Gonal F, Serono, Aubnne, Switzerland) 150 IU/day on day 2 of withdrawal bleeding. Serial ultrasound examinations and evaluation of serum E2 levels were used to assess ovarian response, and then gonadotropin dose adjustments were done as required. Human chorionic gonadotropin (pregnyl, Organon, Oss, the Netherlands ) 10,000 IU was administered when at least two follicles reached a mean diameter of 18 mm.