<prompt> Which of the following tests on maternal serum is most useful in distinguishing between open neural tube defects and ventral wall defects in a fetus?Carcinoembryogenic antigenSphingomyelinAlpha-feto proteinPseudocholinesterase  <response>: In patients with elevated amniotic fluid AFP to differentiate between NTD and abdominal wall defect, acetylcholinesterase and pseudocholinesterase are measured: 