Increase in fetal hydration during long-term intraamniotic isotonic saline infusion

The purpose of this study was to determine whether a long-term infusion of saline into the amniotic space alters amniotic fluid volume or fetal fluid balance. Isotonic saline solution was infused continuously at a rate of 1 L/day for 3 days into the amniotic cavity of eight fetal sheep, resulting in an increase in amniotic fluid volume that averaged 50% of the infused volume. This amniotic volume expansion persisted during a 36-hour recovery period. During the infusion, fetal urine flow increased by 600 ml/day and was accompanied by a significant rise in renal electrolyte excretion. Fetal swallowing of amniotic fluid rose in parallel by 600 ml/day and fetal blood volume significantly increased by 5%. Maternal parameters were not changed during the experimental or recovery periods. Thus the present data suggest that direct intraamniotic infusion on a long-term basis in pregnant sheep appears to be an effective method for increasing fetal hydration and amniotic fluid volume.