2.7.3. COS and oocytes retrieval.
infertility
Participants will be assessed again for eligibility on day 2 or 3 of the IVF cycle. The participants will also receive hormonal and ultrasound assessments to ensure the feasibility of COS.Eligible participants will be administrated COS with a Gonadotrophin-releasing hormone antagonist protocol on day 2 or 3 of the menstrual cycle and given recombinant follicle stimulating hormone (Gonal-F, Merck Serono, Switzerland). The starting dose of rFSH will be in a range between 150–225 IU/day, based on the individual baseline characteristics. The COS process will be individualized, and the follow-up dose of rFSH will be adjusted according to the ovarian response during COS every 2 or 3 days. On day 5 or 6 of the ovarian stimulation, gonadotrophin releasing hormone-antagonist (cetrorelix acetate, Cetrotide; Merck Serono, Germany) will be initiated. When more than 2 follicles are at least 18 mm, 250 mg of recombinant human chorionic gonadotrophin will be administered to trigger the final follicular maturation. After 35 to 37 hours, transvaginal ultrasound-guided aspiration is performed. Intracytoplasmic sperm injection will only be performed in cases of severe male factors of infertility.