Amniotic fluid macrophages and the antenatal diagnosis of anencephaly and spina bifida.

The macrophage content of amniotic fluid has been measured and the upper limit of normal on an arbitrary scale is 41. Amongst 65 amniotic fluids collected for antenatal diagnostic studies before 22weeks' gestation there were eight which had macrophage counts ranging from 82 to 6226,three of these were shown to have anencephaly and two spina bifida. The reasons for three apparently false positives are as yet undetermined. Rhesus iso-immunized amniotic fluids were found to have macrophage counts of up to 276 and a possible explanation for this is considered. It is argued that an elevated aminotic fluid macrophage count may indicate a CNS defect or possibly other fetal abnormality.