Frozen-thawed blastocyst transfer in natural cycle increase implantation rates compared artificial cycle.

To analyze global outcomes in frozen-thawed embryo transfer according to endometrial preparation with natural cycle and artificial cycle taking into account the developmental stage of the embryo. Retrospective cohort study, held in a tertiary-care university hospital with 1265 cycles for frozen-thawed embryo transfer of 860 patients, performed between January 2014 and December 2017. A total of 1097 embryo transfers were performed: 163 transfers in natural cycle (N), 531 in artificial cycle: transdermal estrogens and 403 with oral estrogens.