FALSE-POSITIVE AMNIOTIC-FLUID ACETYLCHOLINESTERASE ANALYSIS IN THE 3RD TRIMESTER

Thirty-two third-trimester amniotic fluid samples were studied accordi ng to the indication for amniocentesis, result of acetylcholinesterase (AChE) analysis, and outcome, in order to address the issue of the ef fectiveness of AChE testing late in gestation. The results indicate th at third-trimester AChE analysis is less effective than second trimest er in distinguishing open neural tube defects (ONTDs) and ventral wall defects (VWDs) from other abnormalities. False-positive results occur red in cases of isolated hydrocephaly (four of seven cases), polyhydra mnios, and intrauterine growth retardation (IUGR). Caution is recommen ded in interpreting third-trimester AChE tests, particularly when neit her an ONTD nor a VWD is observed by ultrasound.