GNRH1 and ovarian hyperstimulation syndrome: 1. E2≥5000pg/ml or ≥18 follicles (GnRH-a trigger) on the trigger day;2. E2≥1500pg/ml;3. ≥18 oocytes obtained;4. 1000pg/ml≤E2 ≤ 1500pg/ml on the day after OPU but the patient had mild OHSS symptoms.