The composition of commercially available human embryo culture media.

study questionWhat is the composition of currently available commercial human embryo culture media provided by seven suppliers, for each stage of human preimplantation embryo development? SUMMARY ANSWER: While common trends existed across brands, distinct differences in composition underlined the absence of a clear standard for human embryo culture medium formulation. WHAT IS KNOWN ALREADY: The reluctance of manufacturers to fully disclose the composition of their human embryo culture media generates uncertainty regarding the culture conditions that are used for human preimplantation embryo culture. The critical role of the embryo culture environment is well-recognized, with proven effects on IVF success rates and child outcomes, such as birth weight. The lack of comprehensive composition details restricts research efforts crucial for enhancing our understanding of its impacts on these outcomes. The ongoing demand for greater transparency remains unmet, highlighting a significant barrier in embryo culture medium optimization. STUDY DESIGN, SIZE, DURATION: For this study, 47 different human embryo culture media and protein supplements were purchased between December 2019 and June 2020; they comprise complete media (n = 23), unsupplemented media (n = 14), and supplements (n = 10). Unsupplemented media were supplemented with each available supplement from the same brand (n = 33 combinations). All samples were directly frozen in liquid nitrogen and stored at -80°C until composition analysis. PARTICIPANTS/MATERIALS, SETTING,

methodsWe determined the concentrations of 40 components in all samples collected (n = 80). Seven electrolytes (calcium, chloride, iron, magnesium, phosphate, potassium, sodium), glucose, immunoglobulins A, G, and M (IgA, IgG, IgM), uric acid, alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), and albumin, as well as the total protein concentration, were determined in each sample using a Cobas 8000 Analyser (Roche Diagnostics). Analysis of pyruvate, lactate, carnitine, and 21 amino acids was achieved with Ultra-High Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS/MS). MAIN RESULTS AND THE ROLE OF CHANCE: Our analysis showed that generally, the concentrations of components of ready-to-use human embryo culture media align with established assumptions about the changing needs of an embryo during early development. For instance, glucose concentrations displayed a high-low-high pattern in sequential media systems from all brands: 2.5-3 mM in most fertilization media, 0.5 mM or below in all cleavage stage media, and 2.5-3.3 mM in most blastocyst stage media. Continuous media generally resembled glucose concentrations of cleavage stage media. However, for other components, such as lactate, glycine, and potassium, we observed clear differences in medium composition across different brands. No two embryo culture media compositions were the same. Remarkably, even embryo culture media from brands that belong to the same parent company differed in composition. Additionally, the scientific backing for the specific concentrations used and the differences in the composition of sequential media is quite limited and often based on minimal in vivo studies of limited sample size or studies using animal models. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: We used a targeted approach and performed a selection of tests which limit the composition analysis to this set of analytes. WIDER IMPLICATIONS OF THE

findingsComprehensive disclosure and complete transparency concerning the composition of human embryo culture media, including the exact concentration of each component, are crucial for evidence-based improvements of culture media for human preimplantation embryos. STUDY FUNDING/COMPETING INTEREST(S): This research was supported by ZonMw (https://www.zonmw.nl/en), Programme Translational Research 2 (project number 446002003). M.G. declares an unrestricted research grant from Ferring not related to the presented work, paid to the institution VU Medical Center. The remaining authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER: N/A.