Amniotic fluid analysis in prenatal diagnosis of neural tube defects: a comparison between six biochemical tests supplementary to the measurement of amniotic fluid alpha-fetoprotein

S-100 protein and neuron-specific enolase in amniotic fluid as markers of abdominal wall and neural tube defects in the fetus

The aim of this study was to determine whether there is increased leakage of neuron-specific enolase (NSE) and S-100 protein into amniotic fluid in pregnancies with neural tube defects, since both these proteins are produced by neural tissue, and to compare the value of these substances for detecting such defects with that of the more conventional techniques of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) gel electrophoresis. Amniotic samples from 25 mid-pregnancies (15-17 weeks' gestation) with neural tube defects (14 with open spina bifida and 11 with anencephaly) and from seven mid-pregnancies with abdominal wall defects were compared with a control material consisting of 80 amniotic fluid samples from 80 consecutive mid-pregnancy amniocenteses, with normal karyotypes and AFP concentrations. All of the above cases of abnormalities were primarily detected through increased AFP levels in the amniotic fluid. Amniotic fluid samples from 13 pregnancies with fetuses with autosomal chromosomal abnormalities and seven amniotic fluid samples contaminated with blood were also included in the investigation. It is concluded from the results that the conventional AFP assay combined with AChE gel electrophoresis is the best method for screening amniotic fluid for neural tube defects and defects of the abdominal wall. Neither NSE nor S-100 assay alone proved to be superior for the detection of these cases in mid-trimester amniotic fluid. The S-100 assay, however, could give additional information in cases where AChE gel electrophoresis is not decisive; for example, in samples contaminated with blood.

Con A non-reactive fractions of human amniotic fluid alpha-fetoprotein in prenatal diagnosis of fetal neural tube defects and fetal abdominal wall defects. Predictive values, sensitivity, and specificity, and comparison to acetylcholinesterase and ultrasound scanning

During a 6-year period 19,647 consecutively received amniotic fluid samples were analyzed for the alpha-fetoprotein (AFP) concentration. In samples with an AFP concentration above the 95% upper normal limit the fraction of AFP non-reactive with concanavalin A (con A) was determined by crossed affinity immunoelectrophoresis. Of 436 samples from normal pregnancies with a moderate elevation of AFP (between the 95% limit and 2.5 times the median) the con A fraction was normal in 92 to 98% of the cases, depending on the gestational age. At significantly elevated AFP concentrations (above 2.5 times the median), the fractions were normal in 78% of the 50 cases with a normal outcome. In 80 of 89 cases of fetal malformations, abnormally low fractions were found, and in all 19 cases of abdominal wall defects and congenital nephrosis the fractions were low. No significant difference was found in the sensitivity for detection of fetal malformations by con A analysis compared to quantitative analysis for acetylcholinesterase (AChE). However, significantly more false positive results were found in normal pregnancies for the con A analysis compared to the AChE analysis. Both analyses performed significantly better than ultrasound scanning in terms of sensitivity. It is concluded that AChE is the test of choice in prenatal diagnosis of fetal neural tube defects. However, a sensitivity of 1.00 and a predictive value of a negative test of 1.00 were found for the con A analysis for fetal abdominal wall defects. The AchE analysis performed less well in this context.

Neurone specific enolase in amniotic fluid: a potential marker of anencephaly

Normal values for neurone specific enolase in amniotic fluid have been found to follow a non gaussian distribution with a 1-99 centile range of 1.10-4.32 micrograms/L. Neurone specific enolase levels have been shown to be raised in the amniotic fluid of pregnancies complicated by anencephaly, although not those complicated by open spina bifida. Neurone specific enolase measured by radioimmunoassay is capable of totally discriminating between normal pregnancies and those complicated by anencephaly. The study demonstrates the possible value of investigating other neuronal proteins which may find value as adjuncts to amniotic fluid Alpha fetoprotein levels in the prenatal diagnosis of Neural Tube Defects.

The association of congenital skin disorders with acetylcholinesterase in amniotic fluid

We describe a fetus with epidermolysis bullosa dystrophica and a fetus with aplasia cutis congenita who were normal by careful ultrasound examination but whose midtrimester amniotic fluids exhibited elevated concentrations of alpha-fetoprotein and presence of acetylcholinesterase. These cases show that serious fetal skin pathology can be a source of amniotic fluid acetylcholinesterase and elevated alpha-fetoprotein concentration and should be considered as part of the differential diagnosis of these amniotic fluid findings.