Fetoproteins are proteins produced by the developing fetus during pregnancy. The most well-known fetoprotein is alpha-fetoprotein (AFP), which is primarily made in the liver. AFP levels can be measured in the mother's blood and are often used as a marker for certain conditions, including neural tube defects and some types of cancer. In addition to their role in fetal development, fetoproteins can also be found in adults, particularly in certain diseases. Elevated levels of AFP in adults may indicate liver conditions, such as hepatocellular carcinoma, or germ cell tumors. Monitoring these proteins can aid in diagnosis and treatment planning.