Prenatal diagnosis of neural tube defects: experiences with acetylcholinesterase gel electrophoresis.

We assessed the qualitative test for AChE in addition to AFP for the diagnosis of NTD in 420 AF samples selected from 16,000 second trimester amniocenteses. Three-hundred and thirty were from normal and ninety from abnormal pregnancies. There were three false positives by this test, two from stored samples containing fetal blood and one from a clear specimen; all had normal outcomes and two had had abnormal AFPs. Forty-seven of forty-seven NTDs were positive by AChE and included 26 cases of anencephaly, 16OSBs, and 5 encephaloceles. In addition, about half of the cases of omphalocele, fetal demise, cystic hygroma, and hydrops gave positive results. One case of congenital nephrosis was negative. We conclude that AChE gel electrophoresis is a useful adjunctive test when AFP levels measure +3 SD above the mean. Although no false negative occurred in this series identified by elevated AFP or increased risk for NTDs, the number in unselected pregnancies is not known.