Human embryonic stem cells as a model for early human development.

Although, the study of human development--from fertilized egg to mature embryo--is extremely important, the early differentiation of human tissues remains an enigma. Moreover, the relatively high percentage of unexplained pregnancy loss--a major concern of human embryologists and gynaecologists--emphasizes the need for an appropriate model for studying early human development. The availability of human pluripotent stem cells might allow us to study previously inaccessible basic processes that occur during human embryogenesis, such as gastrulation and organogenesis.