Prophylactic amnioinfusion was assessed in term and postdates pregnancies with decreased amniotic fluid volume. Subjects were randomly assigned to one of three groups: amnioinfusion with warmed saline solution, roomtemperature saline, or control. Patients receiving prophylactic amnioinfusion had a significant decrease in both the frequency and severity of variable decelerations in the first stage of labor (P=.006) and in the average total number of variable decelerations in the first and second stages of labor (P=.01) compared with controls. There was no observed effect on newborn serum electrolyte levels with amnioinfusion, nor was there any apparent benefit of infusion of warmed saline compared with room-temperature saline. In contrast to premature gestations with oligohydramnios, prophylactic amnioinfusion was not associated with a significant improvement in mean umbilical arterial and venous pH or a significant decrease in cesarean delivery for fetal distress (P=.09). This is perhaps because the term fetus has an enhanced ability to tolerate recurrent episodes of heart rate decelerations without demonstrating the rapid metabolic changes seen in the premature fetus.