Hydrogen Ion Concentration Index of Culture Media

The hydrogen ion concentration index, commonly referred to as “pH,” with “p” derived from the German word “Potenz” and “H” for hydrogen ion. The pH is the ratio of the total count of hydrogen ions to the total amount of substance in a solution. Its value depends on the binding of compounds in the solution and various factors that affect the hydrogen ion equilibrium. The pH value is dynamic, and the process of pH change in a particular aqueous solution during in vitro culture can be roughly divided into three phases: equilibration, set value, and stabilization (Fig. 4.1) [1]. It is worth noting that pH results from a logarithmic calculation, and a slight change in pH means a considerable change in H+ concentration. The acceptable pH range for an embryo culture medium is between 7.2 and 7.4, and there is a 60% difference in H+ concentration between the two—a difference could result in dramatic effects on oocytes and embryos. Therefore, pH changes in the culture system should be minimized and continuously monitored, and pH stability is essential to quality management in the embryo laboratory.