Flexible GnRH Antagonist Embryo Transfer

For PPOS protocols, whole embryos were frozen. For the flexible GnRH antagonist group, three days after oocyte retrieval, one or two embryos were transferred under monitoring by abdominal ultrasound or single blastocyst transfer was carried out five days after oocyte retrieval. For cases with severe ovarian hyperstimulation syndrome (OHSS), an endometrial thickness ≤7 mm, progesterone levels ≥2 ng/ml on the hCG trigger day and the presence of uterine fluid, we canceled the fresh embryo transfer, cryopreserved all embryos and subsequently performed frozen embryo transfer (FET). Endometrial preparation for FET was performed by means of the natural cycle for women with regular menstrual cycles and spontaneous ovulation; artificial/induced ovulation cycle for women with irregular menstrual cycles; and downregulation + an artificial cycle for women with endometriosis. Follicle and endometrial scanning was performed by vaginal ultrasound, and embryo or blastocyst transfer was performed using abdominal ultrasound after 3 or 5 days of endometrial development with luteosterone. Routine corpus luteum support, namely, oral dydrogesterone (2 times daily, 10 mg once) (Abbott Co. America) and intravaginal administration of 90 mg of a progesterone sustained-release vaginal gel (Merck Co. Germany), was given. Corpus luteum support was continued at least until 55 days after transfer if pregnancy occurred.