biostudies-literatureUnknown24(1)Sun Y<h4>Background</h4>This study was designed to evaluate pregnancy outcomes between morulae transferred on day 4 (D4) and blastocysts transferred on day 5 (D5).<h4>Methods</h4>From September 2017 to September 2020, 1963 fresh transfer cycles underwent early follicular phase extra-long protocol for assisted conception in our fertility center were divided into D4 (324 cases) and D5 (1639 cases) groups, and the general situation and other differences of patients in both groups were compared. To compare the differences in pregnancy outcomes, the D4 and D5 groups were further divided into groups A and B based on single and double embryo transfers. Furthermore, the cohort was divided into two groups: those with live births (1116 cases) and those without (847 cases), enabling a deeper evaluation ofBMC pregnancy and childbirth458https://www.ebi.ac.uk/biostudies/studies/S-EPMC11223283biostudies-literatureComparison of pregnancy outcomes between 4th day morula and 5th day blastocyst after embryo transfer: a retrospective cohort study.PMC11223283Xi HShen QFu YSui LSun YZhao JfalseComparison of pregnancy outcomes between 4th day morula and 5th day blastocyst after embryo transfer: a retrospective cohort study.<h4>Background</h4>This study was designed to evaluate pregnancy outcomes between morulae transferred on day 4 (D4) and blastocysts transferred on day 5 (D5).<h4>Methods</h4>From September 2017 to September 2020, 1963 fresh transfer cycles underwent early follicular phase extra-long protocol for assisted conception in our fertility center were divided into D4 (324 cases) and D5 (1639 cases) groups, and the general situation and other differences of patients in both groups were compared. To compare the differences in pregnancy outcomes, the D4 and D5 groups were further divided into groups A and B based on single and double embryo transfers. Furthermore, the cohort was divided into two groups: those with live births (1116 cases) and those without (847 cases), enabling a deeper evaluation of2024-01-01T00:00:00Z2024 Jul2025-04-06T00:13:03.832Z2025-04-06T00:13:03.832ZS-EPMC112232833896135910.1186/s12884-024-06597-7