Amniotic fluid gel cholinesterase density ratios in fetal open defects of the neural tube and ventral wall.

Densitometry was used to measure gel acetyl- and pseudocholinesterase bands in a selection of amniotic fluid samples yielding positive alpha-fetoprotein and positive gel acetylcholinesterase results. The samples were associated with the following conditions: 28 anencephaly (10 stained with fetal blood), 20 open spina bifida (3 stained with fetal blood), 10 open ventral-wall defects (2 stained with fetal blood) and 5 unaffected pregnancies (all stained with fetal blood). In samples not visibly stained with fetal blood, the ratio of the acetylcholinesterase density to the pseudocholinesterase density distinguished between open ventral-wall defects and open neural-tube defects: the former group all had values less than 0.13, while the latter all had values greater than that. In amniotic fluid samples which were stained with fetal blood the acetylcholinesterase/pseudocholinesterase ratio did not offer useful diagnostic information; results from unaffected pregnancies overlapped with those from pregnancies with both ventral-wall defects and open neural-tube defects.