Ratio of amniotic fluid acetylcholinesterase to pseudocholinesterase as an antenatal diagnostic test for exomphalos and gastroschisis.

Amniotic fluid samples from eight pregnancies associated with exomphalos or gastroschisis and 24 with open spina bifida were used to confirm the hypothesis that when the alpha-fetoprotein and gel acetylcholinesterase tests are positive in an amniotic fluid not visibly contaminated with blood, the two defects can be distinguished by scanning densitometry of the electrophoretic gel. The ratio of the density for the acetylcholinesterase band in the gel to that of the pseudocholinesterase band was less than or equal to 0.10 for the open abdominal wall defects and 0.27 or more for open spina bifida. Based on this and a previously reported series, a cut-off level of about 0.15 is suggested.