THE ROLE OF THE FETUS IN THE WATER EXCHANGE OF THE AMNIOTIC FLUID OF NORMAL AND HYDRAMNIOTIC PATIENTS*

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Abstract
The quantity of water transferred between amniotic fluid, fetus and mother has been determined by means of isotopic tracers. Deuterium (D) oxide and tritium (T) oxide were injected into the amniotic sac of pregnant women. From the isotope content of cord blood obtained at cesarean section the time-activity curve for the fetal compartment could be reconstructed. The 6 transfer rates between the 3 hypothetical compartments were calculated. Early in pregnancy the exchange between amniotic fluid and mother is about the same as the exchange between mother and fetus. Later, the role of the fetus becomes more significant. At term the exchange of water between fetus and mother amounts to 3.5 I/hour and 40% of the water transfer from amniotic fluid to maternal organism is accomplished through the intermedium of the fetus. Identical studies on hydramniotic patients indicated a smaller exchange rate between mother and fetus. D and T analyses of organs obtained from non-viable fetuses indicated a satisfactory equilibration within 20-30 minutes. Fetal urine contained appreciable quantities of tracers. Wharton''s jelly had an isotope concentration several times higher than that of cord blood. This was thought to indicate that water transfer between amniotic fluid and fetus takes place through the cord.