In vitro development and metabolism of the human embryo up to the blastocyst stage

The preimplantation period begins with the fertilisation of the oocyte and ends with the formation of the blastocyst. During this period, several major events occur resulting in an embryo composed of pluripotent cells. These morphological changes correspond to changes in the embryonic metabolism. The cleavage stages are characterised by a low metabolism and the inability of the embryo to metabolise glucose. After the activation of the embryonic genome, there is a surge in the embryonic metabolism with increased demand for ATP. The embryo is then able to metabolise glucose. Recently, the importance of amino acids has been highlighted by experiments with mouse, hamster and bovine embryos. Amino acids have also been reported to benefit human embryo development in vitro. Some growth factors have been shown to play a role in human embryo development too. The importance of lipids or vitamins, however, is poorly investigated. Culture media have been developed to improve preimplantation development, but more information is required for adapting culture condition to embryonic requirements which hopefully will improve the outcome of in vitro fertilisation (IVF).