Effect of different sibling human embryo culture volumes on clinical outcomes: a retrospective cohort study.

OBJECTIVE: Single-embryo culture has been adopted to select viable human embryos for transfer, and several modifications-including adjustments in culture medi-um volume-have been proposed to overcome its lim-itations. This study aimed to evaluate whether different culture volumes affect human embryo development and clinical outcomes. METHODS: This retrospective cohort study included 6,173 individually cultured sibling embryos obtained from 859 normal-responder women who underwent in vitro fertilization (IVF) or intracytoplasmic sperm injec-tion between November 2018 and November 2019 at a single fertility center. The embryos were cultured indi-vidually in 30μl (n=3,271) or 10μl (n=2,902) of Syd-ney IVF medium. Embryo quality on days 2, 3, and 5, embryo utilization rates, and fresh embryo transfer out-comes were compared. RESULTS: No significant differences were observed in embryo utilization rate (35.46 vs. 35.25%; p=0.86) or in the rates of good-quality embryos on day 2 (43.36 vs. 42.66%; p=0.18), day 3 (44.88 vs. 43.31%; p=0.22), or day 5 (18.00 vs. 18.00%; p=0.82). Among 249 fresh embryo transfers, clinical pregnancy rates (37.91 vs. 40.63%; p=0.67) and all other pregnancy-related out-comes were comparable. CONCLUSIONS: Culture volume did not affect embryo quality, embryo utilization rate, or clinical pregnancy rates. These results suggest that varying culture vol-umes does not compromise embryonic developmental competence or clinical outcomes, thus supporting the flexible use of different culture volumes in individual em-bryo culture systems in clinical ART practice.