Comparison of pregnancy and live birth rates between fresh day 5 morula transfer and fresh day 6 blastocyst transfer following extended culture for slow growing embryos.

Purpose: The aim of this study is to evaluate and compare the outcomes of fresh day 5 morula transfers and fresh day 6 blastocyst transfers after extended culture, in women with a whole cohort of slow growing embryos.
Methods: Fresh embryo transfer cycles of patients that underwent intracytoplasmic sperm injection between 2013 and 2020 with a whole cohort of slow developing embryos on 5th day of fertilization were evaluated for this retrospective cohort study. Outcomes of day 5 morula transfers and day 6 blastocyst transfers after extended culture were compared.
Results: Out of 479 patients, day 5 morula transfers were performed to 194 and embryo culturing was extended to day 6 in 285 women. Blastocyst formation was observed in 129 of 285 patients in extended culture group. Implantation rate of day 6 blastocyst transfer group was significantly higher than day 5 morula transfer group (27% vs. 12%, p < 0.001). However, clinical pregnancy (17% vs 15.4%) and live birth rates (14.4% vs 13%) were found similar in day 5 morula transfer and extended culture group per initiated cycle.
Conclusion: Although implantation capacity of day 6 blastocysts seems higher comparing to day 5 morulas, clinical pregnancy and live birth rates are similar among intention to treat population in fresh day 5 morula transfers and day 6 blastocyst transfers after extended culture for women that cohorts consist of only slow developing embryos.
(© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)