Definitions of human fertilization and preimplantation growth revisited

Assisted reproductive techniques and the science of embryology have advanced rapidly over the last decades. The fact that social and moral objectives vary from country to country has resulted in differences not only in legislation, but also in the definition of embryological terms. Among the latest additions to the field has been nuclear transfer technology, which has led to concerns about the possibilities of human cloning. These facts call for a review of gametogenesis and early embryogenesis. The aim of the present paper is to initiate a discussion on terminology with a view to reaching a consensus. As a starting point definitions are proposed for the most important terms.