Positive amniotic fluid acetylcholinesterase: distinguishing between open spina bifida and ventral wall defects.

The ratio of amniotic fluid acetylcholinesterase to pseudocholinesterase was determined by scanning densitometry on 43 amniotic fluid samples with positive acetylcholinesterase associated with open fetal defects. The mean ratio was 0.587 (range 0.204 to 0.979) in 21 amniotic fluid samples from pregnancies affected with open spina bifida and 0.052 (range 0.026 to 0.075) in 12 pregnancies affected with ventral wall defects. These data confirm previous observations and indicate that scanning densitometry of electrophoretic gels is a useful method for distinguishing between open spina bifida and ventral wall defects in the fetus.