ObjectiveTo evaluate if the outcomes of IVF/ICSI in frozen-thawed embryo transfer and fresh embryo transfer cycles differ in relation to cleavage and blastocyst stages.MethodsRetrospective cohort study to compare IVF/ICSI outcomes between fresh embryo transfer and frozen-thawed embryo transfer cycles, according to the stage of embryo development. Analysis was carried out on 443 consecutive embryo transfer cycles performed between January 1st and December 31st, 2014. Women aged up to 38 and submitted to embryo transfer cycles with fresh (n = 309) or frozen-thawed (n = 134) embryos at a private center for assistance in human reproduction were considered for analysis. Results in each group were stratified according to the stage of embryo development: cleavage stage and blastocyst stage. Main outcome measures were implantation rate, clinical pregnancy rate, ongoing pregnancy rate and live birth rate per cycle.ResultsIn the fresh embryo transfer group, for cleavage stage versus blastocyst stage, respectively, implantation rates were 22% and 47% (p = 0.0005); clinical pregnancy rates were 34% and 64% (p = 0.0057); the ongoing pregnancy rates were 30% and 61% (p = 0.0046) and live birth rates were 28% and 55% (p = 0.0148). There were no significant differences in the rates between cleavage and blastocyst stages in the frozen-thawed group, neither between fresh and frozen-thawed cleavage embryo transfers nor between fresh and frozen-thawed blastocyst transfers.ConclusionOur results confirm that blastocyst transfer is better than cleavage stage in fresh embryo transfer cycles. In frozen-thawed cycles, cleavage or blastocyst stages seem to offer similar reproductive outcomes.