Factors of the human embryo culture system that may affect media evaporation and osmolality.

STUDY QUESTION Which lab-related factors impact the culture system's capacity to maintain a stable osmolality during human embryo culture? SUMMARY ANSWER Incubator humidity, the volume of mineral oil, the type of culture media and the design of time-lapse dishes have been identified as important parameters that can cause an impact on media evaporation and consequently osmolality during culture. WHAT IS KNOWN ALREADY Culture medium is a critical component in human embryo culture. Minimizing its evaporation during culture is an adequate strategy to stabilize osmolality and, as a result, improving culture conditions and clinical outcomes. STUDY DESIGN, SIZE, DURATION The studied variables included media composition and supplementation; volume of mineral oil; incubator humidification; and the type of dish and incubator used. Additionally, six time-lapse dish models were compared in their ability to prevent evaporation. PARTICIPANTS/MATERIALS, SETTING, METHODS Dishes were incubated in parallel to analyze osmolality during culture between groups: synthetic oviductal medium enriched with potassium versus human tubal fluid medium; protein versus no protein supplementation; dry versus humid atmosphere; high versus low volume of mineral oil. Additionally, media evaporation was compared between six models of time-lapse dishes with distinct designs, cultured in a joint incubator. Two of them were retested in their corresponding incubator to analyze the dish-incubator fit. Daily osmolality measurements were compared between groups. Linear regression was performed to analyze evaporation rates. MAIN RESULTS AND THE ROLE OF CHANCE Protein supplementation did not significantly affect evaporation. Contrarily, humidity levels inside the incubators, the volume of mineral oil and the type of culture media, played an important role in osmolality stabilization. The design of time-lapse dishes and their recommended preparation protocol heavily influenced their evaporation rates, which were further altered by each incubator's characteristics. Media with initially high osmolalities had a bigger risk of reaching hypertonic levels during culture. LIMITATIONS, REASONS FOR CAUTION While numerous, the studied variables are limited and therefore other factors could play a role in osmolality dynamics, as well. Incontrollable atmospheric factors could also result in some variation in the observed results between different centers and laboratories. WIDER IMPLICATIONS OF THE FINDINGS Published literature has extensively described how hypertonic media may impair embryo development and negatively affect clinical outcomes; therefore, maintaining a stable osmolality during culture should be considered essential. This work is of interest both for embryologists when analyzing their culture system and methodologies, as well as manufacturers in charge of designing IVF consumables. STUDY FUNDING/COMPETING INTEREST(S) This study was privately funded. TRIAL REGISTRATION NUMBER N/A.