The question of whether to transfer fresh or frozen embryos and when they can be transferred is asked by many patients, especially for those who have longed for pregnancy, transferring fresh embryos can shorten the waiting time a lot, so is the success rate of transferring fresh and frozen embryos the same? According to a multicenter randomized controlled trial, for patients aged 20-35 years, with menstrual cycles between 21-35 days, normal ovulation, infertility due to tubal or male factors, first time IVF assisted conception, except for history of unilateral oophorectomy, recurrent miscarriage, polycystic ovary syndrome or uterine abnormalities (e.g. endometriosis, submucosal fibroids, uterine adhesions, There was no significant difference in clinical pregnancy rate, persistent pregnancy rate, pregnancy loss rate and live birth rate between the fresh and first cycle frozen embryo transfer groups, but the incidence of moderate to severe ovarian hyperstimulation syndrome was lower in the frozen embryo transfer group than in the fresh embryo transfer group. In another multicenter randomized controlled study, in patients with polycystic ovary syndrome, the live birth rate was significantly higher in the frozen embryo transfer group than in the fresh embryo transfer group, and the incidence of pregnancy loss and ovarian hyperstimulation was lower than in the fresh embryo transfer group, although the risk of preeclampsia was higher in the frozen embryo transfer group than in the fresh embryo transfer group. Therefore, the decision of whether to transfer fresh embryos depends on the status of ovaries and endometrium after egg retrieval. If there is a risk of ovarian hyperstimulation, the condition of endometrium is not suitable for embryo implantation or other combined diseases need to be treated before pregnancy, the whole embryos can be frozen and then transferred at a later date. If there are no contraindications for fresh embryo transfer as mentioned above, the success rate of fresh embryo transfer and frozen embryo transfer is the same. The decision of whether to transfer fresh embryos or frozen embryos needs to be made by the doctor based on the specific situation after egg retrieval.