The presence of increased levels of the following enzyme in amniotic fluid is an indicator of open neural tube defect in the fetus:

Presence of acetylcholinesterase (AChE) in the amniotic fluid is seen in cases of fetal open neural tube defects (NTD). When alpha fetoprotein (AFP) is elevated, an assay for acetylcholinesterase was performed, and if positive, it was considered diagnostic of a NTD. Other fetal abnormalities may be associated with both elevated amniotic fluid AFP and positive assay for acetylcholinesterase, including Ventral wall defects Esophageal atresia Fetal teratoma Cloacal exstrophy Skin abnormalities such as epidermolysis bullosa Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 13. Prenatal Diagnosis and Fetal Therapy. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.