A protein produced in large amounts by the fetal liver, yolk sac, and gastrointestinal tract, whose levels in maternal blood or amniotic fluid help screen for fetal abnormalities. Abnormally high levels can indicate neural tube defects such as spina bifida, while unusually low levels are associated with increased risk of Down syndrome, making it a longstanding component of prenatal screening programs. In adults, elevated alphafoetoprotein serves as a tumor marker, particularly for liver cancer and certain germ-cell tumors, prompting further investigation when found. Nutritionally it has no direct role, but its story intersects with maternal nutrition: adequate folate status reduces neural tube defects, the very conditions this protein helps detect. It remains one of medicine’s most useful circulating proteins for looking backward into fetal development and forward into cancer diagnosis.