Determination of amniotic fluid acetylcholinesterase activity in the antenatal diagnosis of foetal malformations: the first ten years.

The concentration of amniotic fluid acetylcholinesterase activity is elevated in cases of foetal open malformations, the levels being higher in cases of open neural tube defects than in cases of abdominal wall defects. Determination of amniotic fluid acetylcholinesterase activity is an established procedure for the antenatal diagnosis of foetal neural tube defects. Performance data, technical advantages and limitations for three procedures for the determination of acetylcholinesterase activity are reviewed in this paper: an immunoassay, a gel electrophoretic procedure and a spectrophotometric procedure. An immunoassay using the monoclonal antibody 4F19 and the gel electrophoretic procedure show nearly identical diagnostic performances, with detection rates for open spina bifida close to 100% and overall false positive rates of approximately 0.2%. The spectrophotometric procedure is not suitable for the antenatal diagnosis of foetal open neural tube defects and abdominal wall defects. It is possible to distinguish open neural tube defects from abdominal wall defects by determination of the ratio of acetylcholinesterase activity to butyrylcholinesterase activity, either by combining the 4F19 immunoassay with a butyrylcholinesterase immunoassay or by gel electrophoresis followed by densitometry, on samples that display elevated levels of acetylcholinesterase activity.