[Culture media for in vitro fertilization]

The potential of a medium used for IVF-ET must be defined not only by the percentages of successful fertilization and cleavage, but above all by the percentage of term pregnancies. However, they can only be expressed in a well-defined environmental context. The medium has to remain in equilibrium with its gas phase, which can modify the biophysical parameters (pH, pO2, redox potential), and can even be deleterious (presence of NO and CO). Several factors can also interfere with the results obtained in theoretically identical media. In powder media, a certain lack, of homogeneity and an inferior quality of the water added can be major sources of variability. The definitions of the actual compositions of the media can vary continuously and insidiously if the original datum is not consistently taken as reference. These two points are developed in the paper. A great number of facts have, nevertheless, been established: the optimal biophysical conditions, the mineral composition, the amino acid composition, and the necessity for certain substrates such as pyruvate. Numerous lacunae remain: vitamin requirements, the supply of lipids and macromolecular compounds. The addition of serum to the culture media has not helped to remove these uncertainties. We have recently shown that serum is not indispensable in the IVF-ET medium. This opens the way to an understanding of the mechanisms of in vitro fertilization and early embryonic development.