Alpha-fetoprotein (AFP) is a protein produced primarily by the liver of a developing fetus. It plays a crucial role in fetal development, helping to transport nutrients and protect the fetus from the mother's immune system. AFP levels are typically high during pregnancy but decrease significantly after birth. In adults, elevated levels of AFP can indicate certain medical conditions, such as liver disease or specific types of cancer, including hepatocellular carcinoma and germ cell tumors. AFP is often measured through a blood test, which can assist in diagnosis and monitoring of these conditions.