Bulk flows through human fetal membranes.

Bulk water flows across term human amnio-chorion are studied in vitro. The hydrodynamic permeability is found to vary with both hydrostatic and osmotic pressure. The coefficient characterizing flows generated by hydrostatic pressure is substantially larger than that characterizing osmotic flows. The measurements are utilised to predict in vivo bulk flows across the amnio-chorion. These lead to the prediction that at most a flux of 34-83 ml/day may occur across amnio-chorion directed outwards from the amniotic cavity, the principal contribution to this arising from the effects of hydrostatic pressure.