Abstract

Growth during the intrauterine period is a critical determinant of life-long health. During this period the placenta acts as the baby’s life-support system, transferring nutrients and orchestrating maternal adaptations to the pregnancy. But what stimulates formation of the placenta? Development of the human placenta is precocious, and for many years was considered the pinnacle of evolutionary advance amongst mammals by providing early and intimate access to the maternal circulation. Over the last two decades our understanding of the physiology of early pregnancy has undergone radical revision. It is now appreciated that for the first three months the placenta is nourished by the secretory lining of the uterus rather than maternal blood. Furthermore, evidence from domestic species and recently derived human organoid cultures indicates that a signalling dialogue operates between the placenta and the uterus, increasing the release of growth factors and nutrients by the latter. In this way, the placenta stimulates its own development, ready to support the baby. Evidence for this concept will be presented, and the clinical implications discussed.