Live birth after fresh versus frozen single blastocyst transfer (Frefro-blastocyst): study protocol for a randomized controlled trial

Background: Multiple pregnancies are one of the major safety concerns of in vitro fertilization (IVF) due to the increased risk of maternal and neonatal complications. Single embryo transfer is the most effective way to reduce the risk of multiple pregnancies. Selection of the embryo and optimization of the implantation environment are crucial to retain the success rate when the number of transferred embryos is diminished. Fresh embryo transfer with supra-physiological levels of hormones has been suggested to have an adverse effect on implantation. Elective frozen embryo transfer has been suggested to result in a higher rate of live birth than fresh embryo transfer. However, there is still a lack of evidence from randomized clinical trials comparing the efficacy and safety between frozen and fresh single blastocyst transfers. Methods/design: We are conducting a randomized controlled trial in women aged 20-35 undergoing their first cycle of IVF with or without intracytoplasmic sperm injection. After ovarian stimulation with a gonadotropin-releasing hormone antagonist protocol, women who obtain four or more embryos on day 3 of the embryo culture are randomized into two parallel groups: a single fresh blastocyst transfer group and a single frozen blastocyst transfer group (all blastocysts vitrified and a deferred frozen blastocyst transfer). The primary outcome is singleton live birth. Discussion: The results of this study will provide evidence for the efficacy and safety of the strategy of elective frozen single blastocyst transfer in women with a good prognosis.