Frozen embryo transfer: a review on the optimal endometrial preparation and timing

ABSTRACTSTUDY QUESTIONWhat is the optimal endometrial preparation protocol for a frozen embryo transfer (FET)?SUMMARY ANSWERAlthough the optimal endometrial preparation protocol for FET needs further research and is yet to be determined, we propose a standardized timing strategy based on the current available evidence which could assist in the harmonization and comparability of clinic practice and future trials.WHAT IS KNOWN ALREADYAmid a continuous increase in the number of FET cycles, determining the optimal endometrial preparation protocol has become paramount to maximize ART success. In current daily practice, different FET preparation methods and timing strategies are used.STUDY DESIGN, SIZE, DURATIONThis is a review of the current literature on FET preparation methods, with special attention to the timing of the embryo transfer.PARTICIPANTS/MATERIALS, SETTING, METHODSLiterature on the topic was retrieved in PubMed and references from relevant articles were investigated until June 2017.MAIN RESULTS AND THE ROLE OF CHANCEThe number of high quality randomized controlled trials (RCTs) is scarce and, hence, the evidence for the best protocol for FET is poor. Future research should compare both the pregnancy and neonatal outcomes between HRT and true natural cycle (NC) FET. In terms of embryo transfer timing, we propose to start progesterone intake on the theoretical day of oocyte retrieval in HRT and to perform blastocyst transfer at hCG + 7 or LH + 6 in modified or true NC,...
Source: Human Reproduction - Category: Reproduction Medicine Source Type: research