Need for choosing the ideal pH value for IVF culture media

Purpose Monitoring the pH of IVF culture media is a good practice, but the required pH levels have been arbitrarily set. Assisted reproductive technology centers around the world are spending time and money on pH monitoring without any consensus to date. The objective of this narrative review was to evaluate the importance of pH monitoring during IVF, discover how the oocyte and embryo regulate their intracellular pH and try to determine the optimal pH to be applied. Methods A narrative literature review was performed on publications in the PubMed database reporting on the impact of pH on cellular function, oocyte and embryo development, IVF outcomes and pathophysiology, or on physiological pH in the female reproductive tract. Results Intracellular pH regulates many cellular processes such as meiotic spindle stability of the oocyte, cell division and differentiation, embryo enzymatic activities, and blastocoel formation. The internal pH of the human embryo is maintained by regulatory mechanisms (mainly Na+/H+ and HCO3-/Cl- exchangers) that can be exceeded, particularly in the oocyte and early-stage embryos. The opinion that the optimal pH for embryo culture is physiological pH is not correct since several physicochemical parameters specific to IVF culture conditions (temperature, medium composition, duration of culture, or implication of CO2) can modify the intracellular pH of the embryo and change its needs and adaptability. Conclusions Because correct and stable extracellular pH is essential to embryo health and development, monitoring pH is imperative. However, there is a lack of clinical data on choosing the ideal pH for human IVF culture media.