Afterbirth: The placenta + the fetal membranes that are normally expelled from the uterus after the birth of the baby. Hence, the "afterbirth." The placenta is of course the organ that joins the mother and fetus and permits the provision of oxygen and nutrients to the fetus and the release of carbon dioxide and waste products from the fetus to the mother. As humanity only disposable organ, the placenta is disk-shaped and at full term measures about 7 inches (18 cm) in diameter and a bit less than 2 inches (4 cm) thick. The fetal membranes-the chorion is the outer one and the amnion is the inner one - envelop the embryo and contain the amniotic fluid. The word "afterbirth" entered the English language in the 16th century. The term has also been applied to a child born after the father's death or last testament.