Characterization and comparison of commercial oils used for human embryo culture.

STUDY QUESTION: Are there significant differences between the available commercial oil brands used for human IVF? SUMMARY ANSWER: Important differences have been detected among the tested oil brands in their potential to stabilize culture conditions and, more importantly, in their direct effect on embryo development and viability. WHAT IS KNOWN ALREADY: Mineral oil is a critical component of the human culture system due to its protective and stabilizing roles during in vitro embryo development. Many different oils are available on the market, with differences in their viscosity, density and overall quality. STUDY DESIGN, SIZE, DURATION: Thirteen different commercial oil brands were compared. PARTICIPANTS/MATERIALS, SETTING, METHODS: Each oil was firstly analyzed to assess its viscosity, density, peroxide value and potential oxidation. Secondly, the capacity of each oil to reduce pH, osmolality and temperature fluctuations during embryo culture and manipulation was compared. Lastly, a sensitive mouse embryo assay (MEA) protocol, previously optimized to detect toxicity in oils samples, was used to compare the overall quality of the different brands in terms of embryo developmental rates up to the blastocyst stage. At the end of the MEAs, a triple labeling protocol was applied to analyze Oct4+ cells, apoptotic cells and total cell counts in the blastocysts obtained by fluorescence microscopy. MAIN RESULTS AND THE ROLE OF CHANCE: Significant divergences were detected in the rise of osmolality and the equilibration and stability of pH between different oils, which could be correlated to their physico-chemical characteristics. In particular, oil samples with a higher viscosity tended to offer an additional protection against fluctuations in the culture conditions, however, the differences in temperature stability between oils were minor. Two out of the 13 oil samples, which were commercially available, were identified as embryo-toxic by applying the MEA protocol with increased sensitivity for toxicity detection. Additionally, substantial differences in the total number of cells and the number of cells in the inner cell mass of the obtained blastocysts were also detected between oil groups. LIMITATIONS, REASONS FOR CAUTION: A single lot of oil was used for each brand and, thus, lot-to-lot variations in oil quality could not be determined. However, several bottles from the same oil were included to account for potential intra-lot variability. WIDER IMPLICATIONS OF THE FINDINGS: Commercial oils differ in both their physical characteristics and their performance in maintaining the stability of the culture conditions during in vitro embryo culture. Oil selection is important for embryo culture success. Additionally, the detection of embryo-toxic oils which had already been released to the human IVF market showcases the importance of applying sensitive MEA protocols for a better detection of toxicity in this type of samples. STUDY FUNDING/COMPETING INTEREST(S): This study was privately funded. TRIAL REGISTRATION NUMBER: N/A.