Placental iron deposits: significance in normal and abnormal pregnancies.

The extent of iron deposition in the placenta during the various stages of pregnancy, as well as its significance, has not been clearly established. There often is confusion with regard to calcium deposits. To address this issue 82 placentas (60 from normal pregnancies and 22 from abnormal pregnancies) were examined by light microscopy, including iron and calcium stains, and immunoperoxidase stains for ferritin. Seven cases also were studied ultrastructurally, including x-ray microanalysis. With these modalities we could unequivocally differentiate between iron and calcium deposits. It was concluded that in normal pregnancies the placenta stores iron mainly in two forms: first, at least as soon as the seventh week of gestation Hofbauer cells and the syncytiotrophoblast contain ferritin, which is particularly prominent in the syncytiotrophoblast's brush border; and second, during the first two trimesters of gestation iron also is present as linear granular deposits in the trophoblastic basement membrane. In the presence of anomalies in fetal development the iron deposition in the form of linear granular deposits is markedly increased to a statistically significant degree during the second and third trimesters of pregnancy. It is concluded that granular iron deposits in the trophoblastic basement membrane are normally present, gradually decreasing in the progress of normal pregnancies. Their presence in excess (> 7.5% of villi), however, is a pathologic finding associated with fetal growth anomalies.