Results
Overall, 353 FET cycles were performed with HRT were analyzed in this study, including FET of cleavage embryos or blastocysts. All FET cycles were stratified into four groups (P3, P4, P5, and P6) according to the embryonic development stage and the duration of progesterone administration before FET. At the time of analysis, groups P3, P4, P5 and P6 were compared.