The 'Freeze all' strategy, which consists of cryopreservation of all embryos after the ovarian stimulation has undergone extensive development in the past decade. The time required for the endometrium to revert to a prestimulation state after ovarian stimulation and thus the optimal time to perform a deferred embryo transfer after the stimulation has not been determined yet. Objective To investigate the impact of the time from oocyte retrieval to frozen-thawed blastocyst transfer (FBT) on live

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... irth rate (LBR), obstetrical and neonatal outcomes, in 'Freeze-all' cycle. Materials and methods We conducted a large observational cohort study in a tertiary care university hospital including four hundred and seventy-four first autologous FBT performed after ovarian stimulation in 'freeze all' cycles. Reproductive outcomes were compared between FBT performed within the first menstrual cycle after the oocyte retrieval ('cycle 1' group) or delayed FBT ('cycle � 2' group). The main Outcome Measure was the Live birth rate. Result(s)