The placenta is connected to the umbilical cord and attaches to the wall of the uterus.  This organ allows for nutrient exchange and the removal of wastes.  The placenta develops when the blastocyst (embryo) implants into the uterine wall.  Usually this attachment occurs at the superior end of the uterus.  If the placenta grows in the lower part of the uterus, it can obstruct the cervix and birth canal, a condition known as placenta previaplacenta

After the baby is born, the placenta is expelled from the uterus, this is considered “third stage labor.”   The placenta is sometimes called the “afterbirth.”

Fun fact:  Identical twins share a single placenta.  Fraternal twins have their own individual placenta.