ANTENATAL DETECTION OF NEURAL-TUBE DEFECTS - COMPARISON OF BIOCHEMICAL AND IMMUNOFLUORESCENCE METHODS

The aim of this study was to determine whether identification of glial cells in amniotic fluid samples could form a useful supplementary tes t in the antenatal diagnosis of neural tube defects (NTDs). In a 5-yea r study, 1452 samples of middle trimester amniotic fluid were examined blind to the results of other antenatal diagnostic tests and to the o utcome of pregnancy. Reasons for amniocentesis included raised serum a lpha-fetoprotein (329), previous NTD (73), and a family history of NTD s (7 1). Duplicate cytospin preparations were stained with Giemsa and an antibody to glial fibrillary acidic protein (GFAP), and on this bas is a prediction of fetal NTD status was made which was not communicate d to clinicians. Subsequent management of pregnancies was influenced o nly by the results of routine antenatal testing for NTDs. Twenty cases of NTDs occurred among the 1406 cases in which the outcome was subseq uently known. Of these 20 cases, only five (four anencephalic, one spi na bifida) were correctly predicted by immunofluorescent identificatio n of GFAP-positive cells in the amniotic fluid. The remaining 15 cases (two anencephalic, 13 spina bifida) were not so identified. In a furt her 18 cases, apparently GFAP-positive cells were identified in the ab sence of NTDs. We conclude that GFAP immunofluorescence examination of routine amniocentesis samples of amniotic fluid is not a useful predi ctive test for NTDs.