Roelens C, Santos-Ribeiro S, Becu L, et al. - Researchers sought to ascertain the difference in live birth rate (LBR) between frozen-warmed blastocyst transfer (FET) on the 6th or the 7th day of progesterone administration in artificially prepared cycles via performing a retrospective cohort study of patients who underwent FET between December 2015 and December 2017 in a hormone replacement therapy cycle (HRT). Among 619 included patients, 346 underwent transfer of a vitrified-warmed blastocyst on the 6th day of progesterone administration and 273 underwent blastocyst transfer on the 7th day of progesterone. Per outcomes, similar LBRs were evident in correlation with warmed blastocyst transfer on the 6th compared with the 7th day of progesterone administration in an HRT cycle. Subgroup analysis of day 6 blastocysts showed significantly higher miscarriage rates when FET was performed on the 6th day of progesterone administration.