pHantastic Embryos and Where to Find Them: Can a Real-Time pH Monitoring System Represent the pH Environment of Culture Media?

Abstract

Background: Maintaining optimal pH of culture media reduces environmental stressors on gametes and embryos, which has been shown to be critical in supporting embryo development. There are many options to determine pH but none are ideal for use in a laboratory setting. SignipHy™ is a system that monitors pH in real-time within the incubator environment without disturbing the incubator or exposing the media. Aim: To determine if SignipHy can provide an accurate representation of the dynamic pH in culture media across a range of environmental conditions. Method: pH of G1+ under Ovoil in a 5-well dish was measured using a blood gas analyser at regular intervals under multiple experimental conditions. Statistical analyses used repeated measures ANOVA, Pearson’s Correlation and Linear regression. Results: pH of media undergoing initial equilibration was found to decrease more rapidly in culture dishes (ΔpH 0.228/hr) than SignipHy cuvettes (ΔpH 0.160/hr) over a 6 hour period (p=0.0005). Full equilibration was achieved in the culture dishes after 4 hours, while the SignipHy cuvettes stabilised after 6 hours. When fully equilibrated dishes were exposed to 4% CO2, pH in the culture dishes increased more rapidly (ΔpH 0.098/hr) than SignipHy cuvettes (ΔpH 0.060/hr). Similarly, equilibrated media exposed to 2% CO2 showed an increase of pH in culture dishes of 0.171/hr compared with SignipHy cuvettes at 0.150/hr. Unsurprisingly when media in a culture dish without oil was exposed to a humified CO2 incubator the pH shift was rapid (ΔpH 0.258/hr). Laboratories should be conscious of rapid pH shifts in culture media without oil. Which can be optimal when needing to equilibrate media quickly, but of concern when handling dishes. Conclusion: SignipHy was found to be a viable representation of pH under multiple experimental conditions, however, the rate of change was found to be slower compared to culture dishes.