The syncytiotrophoblast forms a continuous barrier between the maternal and fetal circulations. Here we present a serial block‐face scanning electron microscopy (SBFSEM) study, based on a single image stack, showing pooling of fetal blood underneath a region of stretched syncytiotrophoblast that has become detached from the basement membrane. Erythrocytes are protruding from discrete holes in the syncytiotrophoblast suggesting that, under specific circumstances, the syncytiotrophoblast may be permeable to fetal cells. This observation represents a pathological process but it poses questions about the physical properties and permeability of the syncytiotrophoblast and may represent an early stage in the formation of fibrin deposits in areas of syncytial denudation. This study also illustrates how the 3D images generated by SBFSEM allow the interpretation of structures that could not be understood from a single histological section. Introduction The human placenta is monochorionic and haemochorial, and its syncytiotrophoblast forms a continuous barrier between the maternal and fetal circulations (Sibley, ). Despite the continuous nature of the syncytiotrophoblast, there is functional evidence for a size‐selective paracellular route (Sibley,; Bain et al.

Kilauea; Mount Etna; Mount Yasur; Mount Nyiragongo and Nyamuragira; Piton de la Fournaise; Erta Ale. Statistical Techniques Statistical Mechanics.

The anatomical basis for the paracellular route remains unclear, and although trans‐trophoblastic channels have been proposed, they have not been observed to cross the full width of the syncytiotrophoblast. Electronics Components Datasheet Software Update. However, partial channels may have been observed under pressure (Kertschanska et al.

Alternatively, evidence exists for regions of syncytial denudation that may allow paracellular diffusion (Brownbill et al. These regions of syncytial denudation are covered in fibrin deposits whose pathogenesis is not entirely understood. The passive permeability of the placenta decreases with increasing molecular size and proteins and cells would not be expected to cross the placenta (Bain et al.; Sibley, ). Maternal microchimerism demonstrates that non‐trophoblastic fetal cells can enter the mother's circulation (Bianchi et al. In this study, we present evidence that fetal cells could, under specific pathological conditions, cross the syncytiotrophoblast. Methods Tissue was collected after vaginal delivery from term placenta from an uncomplicated pregnancy with written informed consent and ethical approval from the Southampton and Southwest Hampshire Local Ethics Committee (11/SC/0529).

Within 30 min of delivery, a villous sample was dissected out and placed directly into 3% glutaraldehyde in 0.1 m cacodylate buffer at pH 7.4 at room temperature (RT) and stored at 4 °C until processing. Samples were treated twice with 0.1 m sodium cacodylate buffer pH 7.4 containing 0.23 m sucrose and 2 m m CaCl 2 for 10 min, 4% OsO 4 for 60 min, thiocarbohydrazide for 20 min, 2% OsO 4 for 30 min and finally 2% uranyl acetate for 60 min. Samples were embedded in Spurr's resin, polymerised at 60 °C for 16 h, blocks were trimmed (100 μm 2), mounted on an aluminium pin with conductive glue and sputter‐coated with gold/palladium (Holcomb et al. Blocks were imaged using a Gatan 3View inside an FEI Quanta 250 FEGSEM at 3.0 KV accelerating voltage and with a vacuum level of 40 Pa. The voxel size was 22 × 22 × 50 nm, and the total image size was 3000 × 3000 pixels.