IVF protocol
Doctors chose different IVF protocols based on the patient’s age and ovarian reserve. The GnRH agonist and GnRH antagonist protocols have been the main protocol in our center. Controlled ovarian hyperstimulation, oocyte retrieval, embryo transfer, and endometrial preparation for frozen-thawed embryo transfer (FET) were performed as previously described [6,7]. Briefly, for the GnRH agonist, patients used down-regulation from the mid-luteal phase of the previous cycle, recombinant FSH was started at 150-225IU/day when the pituitary had reached desensitization. For the GnRH antagonist protocol, recombinant FSH was initiated on day 2 of the cycle. GnRH antagonist was started when the dominant follicle reached 12-14mm at 250mg/d. When two or more follicles reached 18mm, hCG was administrated at a dose of 4,000 to 10,000. Oocyte retrieval was carried out 34-36 h following hCG trigger. Conventional IVF or intracytoplasmic sperm injection (ICSI) was performed according to the male partner’s semen quality.