Abstract
PURPOSE: While new technologies support undisturbed embryo culture, non-humidified incubation raises concerns about medium stability. High-viscosity oil (HVO) was proposed to maintain osmolality, but its validation remains limited. This study investigates whether HVO offers advantages over conventional light oil (CLO) in preventing evaporation during extended dry incubation using a high-volume media drop setting and its impact on embryo development and temperature control. METHODS: HVO and CLO were overlaid on embryo culture media drops and incubated for 5 days under either dry or humid conditions. At various intervals throughout the experiment, measurements of osmolality, pH, temperature, and sodium concentration were taken. To assess toxicity, mouse embryo assays and lipid peroxidation detection were conducted in post-culture media. RESULTS: The dry incubation significantly increased osmolality and sodium concentrations, regardless of oil type, from the first day of incubation, under the current experimental conditions. After 5 days of incubation, HVO was not superior to CLO in preventing these changes under dry conditions (289.867 ± 1.10 vs. 284.93 ± 1.03, respectively, p > 0.05). The mean osmolality values in CLO vs. HVO in dry conditions provided mild protection against temperature loss when dishes were removed from incubators and exposed to room temperature for 5 min, simulating a suboptimal setting. No significant differences were observed between HVO and CLO regarding lipid peroxidation or embryo development. CONCLUSION: These findings indicate that a high-viscosity oil does not confer better protection against evaporation than a conventional oil when uninterrupted culture is performed in dry incubation and high-volume media drops are used.