ABSTRACT
The goal of in vitro fertilization (IVF) and embryo culture is to provide high quality embryos capable of continued development and implantation, which will result in the birth of healthy babies. Considerable progress has been made in culturing preimplantation embryos since the initial studies were undertaken. We began to design and define new, more complex culture media in the early 1970s, which were based on the composition of genital tract secretions.1 During the initial stages of zygote formation and early cleavage divisions, the cells carry out only a minimal level of transcription, since early preimplantation development, i.e. up to the stage of maternal to zygotic transition (MZT), is maternally driven. A mature oocyte must contain a storage pool of proteins and/or mRNA transcripts in order to maintain its viability during these early stages: all of the enzymes required for metabolic pathways must be present and in harmony with the components of the culture medium. During and after the cycle of MZT, the longest cycle of preimplantation development, transcription of the new zygote genome then results in an increase in mRNA levels. The requirements of the embryo before and after MZT differ, and the environment, i.e. culture conditions, will have a direct impact on transcription and translation. Moreover, epigenetic reprogramming throughout early preimplantation development is also important, and this has generated concerns regarding the role of culture conditions in assisted reproductive technologies.2-6 In this chapter we describe the basis of embryo metabolism, and the impact of culture media composition on embryo quality and viability.
