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BACKGROUND:Frozen-thawed embryo transfer (FET) has become a routine procedure in assisted reproductive technology (ART). In FET, although blastocysts cultured from thawed cleavage-stage embryos are associated with better perinatal outcomes. it may increase cycle cancellation due to no suitable embryo to transfer. The overall clinical outcomes following transfer of thawed cleavage-stage FET and blastocysts cultured from thawed cleavage-stage embryos in young and advanced age patients remains unclear. Therefore, we aimed to identify the optimal FET strategy in young and advanced age women who undergo FET. METHODS:This retrospective study included 16,387 thaw cycles. We retrospectively analyzed data of couples who had completed the first FET cycle. Two FET strategies were studied: transfer of thawed cleavage-stage embryos (strategy A) or blastocysts cultured from thawed cleavage-stage embryos (strategy B). The clinical and neonatal outcomes of two FET strategies were compared in young (<35 years) and advanced (≥35 years) age women. RESULTS:In young women, the clinical outcomes per transfer cycle were better in strategy B than strategy A. While the clinical pregnancy (59.29%, 52.60%) and live birth rates (49.37%, 43.88%) per thaw cycle were significantly higher in strategy A than in B. In women of advanced age, the clinical outcomes per transfer cycle were still better in strategy B than in A, and the clinical pregnancy (36.44%, 39.66%) and live birth rates (25.70%, 30.00%) per thaw cycle were significantly higher in strategy B than in A. CONCLUSIONS:FET of blastocysts cultured from cleavage-stage embryos showed higher efficiency for per transfer cycle whether in younger or advanced age women. Whereas, when cycle cancellations due to no suitable embryo to transfer were considered, cleavage-stage FET was found to be more suitable for younger women, while FET of blastocysts cultured from cleavage-stage embryos was better suited for women of advanced age.