[Acetylcholinesterase of amniotic fluid: application to prenatal diagnosis of neural tube closing defects. I. Quantitative tests].

Acetylcholinesterase (AChE) in amniotic fluid from 165 normal pregnancies and 38 abnormal pregnancies was measured, using a direct assay of AChE activity after inhibition of ChnS with ethopropozine ("Lysivane"). Samples from normal pregnancies of 16-24 weeks gestation have a mean AChE activity of 2,7 U/1 and those obtained at 26-40 weeks have a mean level of 0,6 U/l. Contamination of amniotic fluid with fetal or maternal blood was observed to elevate AChE activity leading to uninterpretable results. Assays in artificial mixtures of amniotic fluid with maternal or fetal blood confirm the risk related to added erythrocyte number. Higher mean AChE activity, 8 U/l, was observed in association with open NTD, but in 7 cases the level was as in normal pregnancy. Elevated levels of AChE were found in association with Turner's syndrome (1) and intra uterine death (2); no increase was observed in 7 cases of omphalocele or laparoschisis, in 6 cases of atresia and 2 cases of hydrocephaly. In practice frequent occurence of bloody samples, specially from abnormal pregnancies, limits application of the test for antenatal open NTD diagnosis. This test appears as and useful preliminary stage providing informations for realization and interpretation of gel electrophoresis of cholinesterases.