Estimation of Water Transfer from Amniotic Fluid to Fetus.

Abstract

The average exchange rate of water between amniotic fluid and the human maternal system amounts to about 27 mols per hour. If the fetus plays a major role in the transfer of water the treatment of experimental data must provide for this by its inclusion as a separate third compartment. Since the human fetus remains inaccessible, except during delivery, the evidence must be derived indirectly. Deuterium oxide was injected into the amniotic sac of pregnant women 1 hour or less before delivery by Cesarean section. The tracer concentration in cord blood invariably exceeded the calculated equilibrium value by 25 -250%. This observation led to the conclusion that time activity curves for the fetal compartment must pass through a maximum. On the basis of experiments with hydrodynamic models this was interpreted to mean that at least 25%, probably more than 50% , of the water transfer from the amniotic fluid to mother is accomplished through the intermedium of the fetus.