PPOS vs GnRH Antagonist in Ovarian Stimulation (ProGanOS Study)

Study Procedures Participants will be randomized into two arms: * PPOS group: Recombinant FSH 150-300 IU/day will start from day 2 to day 4 of menstruation. The initial FSH dose will be chosen based on age, anti-Müllerian hormone (AMH) level, antral follicle count (AFC), and body mass index (BMI). The FSH dosage will be fixed during ovarian stimulation. Dydrogesterone (Duphaston, Abbott, USA) 20mg/day will start on the day of gonadotropin injection to the oocyte maturation trigger night. * GnRH antagonist group: Recombinant FSH 150-300 IU/day will be given from day 2 to day 4 of menstruation. The initial FSH dose will be chosen based on age, anti-Müllerian hormone (AMH) level, antral follicle count (AFC), and body mass index (BMI). The FSH dosage will be fixed during ovarian stimulation. Cetrorelix (Cetrotide, Merck, Germany) 0.25mg/day will be given from day 5 of stimulation by the oocyte maturation trigger day. Follicular monitoring will start on the fifth or sixth day of ovarian stimulation and was performed every 3-5 days thereafter using transvaginal ultrasound to record the number of developing follicles. Measuring LH, estradiol, and progesterone serum levels will be performed on the fifth or sixth day of ovarian stimulation and oocyte maturation day (before the trigger injection). The FSH dosage will be fixed during ovarian stimulation. When more than two dominant follicles reach a diameter of at least 17mm, \>= 50% diameter of remaining follicles cohort \>=12 mm, the final stage of oocyte maturation will trigger using human chorionic gonadotropin (hCG; IVF-C 10.000 IU, LG Chem, Ltd., Korea or Ovitrelle Pen 250µg, Merck Serono S.p.A., Italy). In individuals who are at high risk for OHSS, GnRH agonist trigger 0.2mg (Diphereline 0.2mg, Ipsen Pharma, France) will given subcutaneously. Transvaginal ultrasound-guided oocyte retrieval will be performed 34-36 hours after trigger, with the retrieval of all follicles exceeding 10mm in diameter. Oocyte fertilization will be carried out in vitro using ICSI. On the third day after fertilization, embryos will be evaluated for the degree of embryonic fragmentation, regularity, and number of blastomeres in accordance with the Istanbul consensus (Alpha Scientists in Reproductive Medicine and ESHRE Special Interest Group of Embryology, 2011). Day 3 embryos will be cryopreserved or cultured until the blastocyst stage based on physician recommendation or patient references; viable blastocysts will then be cryopreserved on day 5 or day 6. Endometrial preparation for frozen embryo transfer (FET) will be given using an exogenous steroid regimen from day 2 to day 4 of the menstrual cycle. Oral estradiol valerate (Progynova, Bayer Schering Pharma, Germany) 8mg/day will be given for 10-12 days. When endometrial thickness reaches ≥ 7mm, along with a triple-line pattern, micronized progesterone 800mg will be administered. FET will be performed three to five days after progesterone administration. There will be no more than 2 embryo(s) transfers each FET cycle. After FET, estradiol and progesterone supplementation will be continued for all participants until the day of taking the pregnancy test. Participants with a positive pregnancy test continued to receive oral estradiol valerate 8mg/day and micronized progesterone 800mg/day until the fetal heart appeared, and then only micronized progesterone 800mg will be used until 12 weeks of gestation. All participants will be followed up per local protocol until outcomes are achieved.