Test-tube embryos - mouse and human development in vitro to blastocyst stage and beyond.

Mammalian embryogenesis is intrauterine and depends on support from the maternal environment. Therefore, in order to directly study and manipulate early mouse and human embryos, fine-tuned culture conditions have to be provided to maintain embryo growth in vitro. Over time, the establishment and implementation of embryo culture methods have come a long way, initially enabling the development of few pre-implantation stages, expanding later to support in vitro embryogenesis from fertilization until blastocyst and even ex utero development beyond the implantation stages. Designing culture conditions that enable near physiological development of early embryos without maternal input, especially during the peri- and post-implantation stages, requires overcoming numerous experimental challenges, and it is still far from optimal. Nevertheless, embryo culture methods are an essential cornerstone of both assisted reproductive technologies and basic research, and these methods provide a platform to understand life's greatest miracle - the development of a new organism.