Effect of maternal hydration on oligohydramnios: a comparison of three volume expansion methods

Abstract

Objective: To determine the effect of maternal hydration with intravenous (IV) isotonic fluid, IV hypotonic fluid, and oral water on amniotic fluid index (AFI) in women with oligohydramnios. Methods: Patients with low AFI and gestational age over 35 weeks without maternal complications were randomized into four groups (2 L/2 h IV isotonic fluid, 2 L/2 h IV hypotonic fluid, 2 L/2 h oral water, control). Maternal plasma osmolality, AFI, hematocrit, and hemoglobin concentration were measured before and after hydration. Results: Eighty-four patients ( n = 21/group) completed the study without any maternal adverse effects. The mean increase in AFI after hydration was significantly greater in the IV hypotonic and oral water groups (2.8 ± 1.9, P < .001; 3.8 ± 1.9, P < .001, respectively), but not in the IV isotonic group (0.5 ± 1.1), compared with the control group (0.5 ± 1.1). Significant decreases in maternal hematocrit and hemoglobin concentration were found only after IV isotonic hydration (32.0 ± 2.9 to 29.5 ± 2.3, P < .001; 11.0 ± 1.6 to 10.1 ± 1.4, P < .001, respectively). Changes in maternal osmolality correlated with the changes in AFI in both the IV hypotonic group ( r = .58, P < .001) and oral water group ( r = .63, P < .001). Conclusion: Maternal hydration with either IV hypotonic fluid or oral water increases AFI in oligohydramnios. Maternal osmotic change rather than maternal volume expansion had a more direct impact on increasing amniotic fluid volume with short-term acute hydration.