Ovarian stimulation protocol
An antagonistic regimen was administered to all patients (a flexible antagonist regime) for controlled ovarian stimulation. Prior to the ovarian stimulation cycle, all patients received OCPs (Ovocept LD, Abureihan, Iran) for 21 days. Briefly, 150–300 IU/day of recombinant follicle-stimulating hormone (Gonal-F, Merck Serono SA, Switzerland) was prescribed from the third day of the menstrual cycle. The optimum dosage was set considering the estradiol concentration and ovarian response. After monitoring the ovaries, when at least 2 follicles with the size of 14–15 mm were present, 0.25 mg/day cetrorelix acetate, Cetrotide (Merck Serono SA, Switzerland) was administered as the gonadotropin-releasing hormone antagonist. Cetrotide consumption was discontinued after reaching a diameter of 18 mm ≥ 2 for follicles; however, 10,000 IU human chorionic gonadotropin (hCG) was administered (Ovitrelle, Merck Serono SA, Switzerland), and oocytes were retrieved after 36 h through transvaginal ultrasound-guided aspiration