Female Anatomy: The Uterus and Amniotic Sac
There are a few different parts of a woman's body (the female reproductive anatomy) that are involved with pregnancy and labor. The uterus, also called the "womb," is a pear-shaped organ that rests above the vagina, or birth canal. During pregnancy, the uterus stretches and expands along with the growing baby. Although the baby's position will vary throughout the pregnancy, almost all babies are in a head-down position as the mother's due date gets closer.
The baby grows inside the uterus in a balloon-like sac, called the amniotic sac. This sac is filled with amniotic fluid, which is mostly water.
The placenta, which is also known as the "afterbirth," is a sponge-like layer between the amniotic sac and the inside of the uterus. The placenta contains two sets of blood vessels -- one set from the mother and one from the growing baby. These vessels are close enough together that food and oxygen from the mother's blood can easily move into the baby's blood, where they provide essential nutrients for the baby to grow. The nutrients travel from the placenta to the baby through a blood vessel in the umbilical cord, which enters the baby's navel.
As the baby grows, the natural waste products that are produced need to be cleared from the baby's blood. These waste products travel through the baby's blood vessels to the placenta and are transferred to the mother's blood. The waste products are then eliminated from the mother's body.