Final answer:
The term "after birth" primarily refers to the placenta, which is delivered after the baby's birth and supports the fetus during pregnancy by exchanging nutrients and gases through the umbilical cord.
Step-by-step explanation:
The phrase "after birth" primarily refers to the placenta, which is the structure that develops during pregnancy to provide oxygen, nutrients, and waste removal for the developing fetus. After a baby is born, the placenta, which was attached to the lining of the mother's uterus, is also delivered, hence the term "afterbirth." The placenta is a critical component of fetal development, as it serves as the interface for the exchange of nutrients and gases between the mother and the fetus through the umbilical cord. It is important to note that the amniotic sac is different from the placenta. The amniotic sac is a membrane that surrounds and protects the fetus in the womb, filled with amniotic fluid.