Amniotic fluid volume and its relationship to fetal fluid balance: review of experimental data.

The studies described above collectively suggest that, whenever there is a decrease in fluid balance in the fetus, both fetal urine flow and tracheal secretion into the amniotic space are decreased. Conversely, when fetal hydration is increased, both urine and tracheal flows into the amniotic fluid may be increased. These observations suggest the hypothesis that, except under pathological conditions, aberrations in amniotic fluid volume may be the consequence of the existing state of hydration of the fetus. In addition, it appears that under many circumstances, these deviations from normal in fetal fluid balance may be due to maternal influences. Of course, the concept that fetal fluid balance is the primary factor determining amniotic fluid volume needs to be modified to incorporate transmembrane fluxes. However, these fluxes have yet to be documented as they relate to amniotic fluid volume and its regulation.