Human Placenta Project: How Does the Placenta Form? | NICHD - Eunice Kennedy Shriver National Institute of Child Health and Human Development

Human Placenta Project: How Does the Placenta Form? | NICHD - Eunice Kennedy Shriver National Institute of Child Health and Human Development: The illustrations below show how the human placenta develops. The timeline of placental development shows how the placenta changes over the course of pregnancy. A crucial stage of placental development is when blood vessels in the lining of the uterus are remodeled, increasing the supply of blood to the placenta. This process, called spiral artery remodeling, is also illustrated in close-up.