Which protein is tested for in maternal serum testing for fetal anomalies?

• A. Free beta-hCG
• B. Estriol
• C. Alpha fetal protein (AFP)
• D. Inhibin A

Answer: (C)

Maternal serum alpha-fetoprotein is the marker used to screen for fetal open neural tube defects. AFP is produced by the fetal liver and yolk sac and passes into the mother’s blood; elevated levels in the second trimester (about 15–20 weeks) raise concern for neural tube defects such as spina bifida or anencephaly, and for ventral wall defects like omphalocele or gastroschisis. False positives can occur from dating errors, multiple gestation, or fetal demise, so follow-up ultrasound to confirm gestational age and anatomy is important, and if indicated, amniocentesis to measure amniotic fluid AFP and acetylcholinesterase can help confirm neural tube defects. The other markers listed are used more for screening fetal chromosomal abnormalities rather than neural tube defects.