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1. Introduction
Since 1978, about 10 million children all over the world were born after applying assisted reproduction technique (ART). Therefore, 1–3% of all babies born in developed countries result from the use of ART. Besides optimizing the technique of ART to improve pregnancy rates, it is also important to consider risks of the therapy itself as well as possible long-term consequences for those children. Although human IVF procedure is constantly improved by implementation of innovative techniques and new scientific results regarding the preimplantation development, the current methods do not succeed in mimicking the in vivo situation completely. Therefore, knowledge about factors which regulate the preimplantation development is of great interest.
The components of the medium in which the embryo is cultured as well as the oxygen concentration of the in vitro culture play important roles in mimicking the female reproductive tract and therewith influence the gene expression of the preimplantation embryo [1, 2]. Development of the sequential media system already respects the changing metabolism of the preimplantation embryo with regard to glucose concentration, amino acids, and ph within its development to a blastocyst [3]. Physiologically, the preimplantation embryo develops in hypoxic condition within the reproductive tract (oxygen concentration: oviduct 8%, uterus 1.5%) whereas in vitro embryos are cultured with atmospheric oxygen tension (oxygen concentration: 20%). High oxygen concentration results in generation of reactive oxygen species (ROS). Besides the capability of ROS to damage cell function by modifying the structure of lipids, proteins and DNA causing strand breaks and inactivation of enzymes, ROS serve as key signalling molecules in physiological processes and are essential for embryogenesis by regulating cell proliferation and intracellular signal transduction pathways. In order to optimize the in vitro culture system, the oxygen concentration might be reduced by either culturing the embryo under hypoxic conditions or by adding antioxidants to the culture media.
The early embryo development from the zygote to the blastocyst stage and the implantation are complex processes with morphological and dynamic changes in the surrounding and the metabolism of the embryo. A large number of genes are involved in...