Which fetal protein is commonly used as a marker for neural tube defects due to elevated levels in amniotic fluid?

• A. a1-Antitrypsin
• B. a1-Acid glycoprotein
• C. a1-Fetoprotein
• D. a2-Macroglobulin

Answer: (C)

Alpha-fetoprotein is a fetal protein produced by the liver and yolk sac. It normally appears in the fetal circulation and in amniotic fluid at low levels, but when there is an open neural tube defect such as spina bifida or anencephaly, the barrier between fetal serum and amniotic fluid is compromised, allowing AFP to leak into the amniotic fluid and elevate its level. This elevation in amniotic fluid makes alpha-fetoprotein the go-to marker for neural tube defects. It’s also used in maternal screening programs where high levels raise suspicion and lead to further testing. The other proteins listed are not markers for neural tube defects and don’t reflect fetal neural tube status.