Angiogenesis and implantation.

Mammalian implantation is a complex, but still poorly understood, process in which the developing embryo establishes contact with the endometrial surface epithelium before developing a haemochorial placenta. The growth and development of the placenta and its subsequent invasion into the decidua can be likened to the invasion of healthy tissue by malignancy. The establishment of an angiogenic phenotype is a critical event in the progression of benign disease to malignant. Little is known about the role of angiogenesis in implantation but in view of the importance of vascular development to the receptive endometrium, angiogenesis is likely to be critical for successful implantation. Here, the factors that control the development of blood vessels in the pre-implantation phase are reviewed and the complex interplay between the embryo and decidua that leads to the establishment of a healthy placenta is considered.