AFP is used as a tumor marker to help detect and diagnose cancers of the liver, testes, and ovaries.It is regularly done in patients of liver cancer  periodically to help monitor the person's response to therapy and to monitor for cancer recurrence. AFP Maternal serum screening is used in the second trimester of pregnancy to help evaluate the risk that a fetus has certain chromosomal abnormalities, including Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18), or neural tube defects such as spina bifida or a condition called anencephaly.