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

To determine the effect of maternal hydration with intravenous (i.v.) isotonic fluid, i.v. hypotonic fluid, and oral water on amniotic fluid index (AFI) in women with oligohydramnios.Patients with low AFI and gestational age over 35 weeks without maternal complications were randomized into four groups (2 L/2 h i.v. isotonic fluid, 2 L/2 h i.v. hypotonic fluid, 2 L/2 h oral water, control). Maternal plasma osmolality, AFI, hematocrit, and hemoglobin concentration were measured before and after hydration.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 i.v. hypotonic and oral water groups (2.8+/-1.9, P < .001; 3.8 +/-1.9, P < .001, respectively), but not in the i.v. 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 i.v. 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 i.v. hypotonic group (r=.58, P < .001) and oral water group (r =.63, P < .001).Maternal hydration with either i.v. 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.