Reduced blastocyst formation in reduced culture volume

The aim of this prospective sibling oocyte study was to evaluate whether reduced culture volume improves blastocyst formation. Twenty-three patients with extended embryo culture until day 5 were selected for the study. After injection, 345 sibling oocytes were individually cultured in either 25 or 7 mu l droplets of Origio cleavage medium under oil. On day 3 of development, embryos were transferred to droplets with the corresponding volume of Origio blastocyst culture medium. Fertilization and embryo quality on day 3 and day 5/6 were evaluated. No statistically significant difference (p = 0.326) in fertilization rate was observed (81.3 versus 83.0 %). There was no significant difference in terms of the number of excellent and good-quality embryos obtained on day 3 between both groups (p = 0.655). Embryo culture in 25 mu l droplets led to more embryos with a higher cell number when compared to 7 mu l culture (p = 0.024). On day 3, 132 and 131 embryos were considered for further culture until day 5/6. Blastulation rates were significantly higher in the 25 mu l group (75.0 versus 61.6 %; p = 0.017) and significantly more day 5 embryos with excellent and good quality were found in this group (54.5 versus 40.5 %; p = 0.026). Finally, the utilization rates expressed per mature oocyte (41.4 versus 29.8 %; p = 0.043), per fertilized oocyte (50.7 versus 36.6 %; p = 0.023), and per day 3 embryo undergoing extended culture to day 5/6 (54.5 versus 39.7 %; p = 0.019) were all significantly higher in the 25 mu l group. Reduced culture volume (7 mu l) negatively impacts early development by reducing the cell number on day 3 and both blastocyst formation and quality.