The Effect of Immersion on Haemodynamic and Fetal Measures in Uncomplicated Pregnancies of Nulliparous Women

When a standing or sitting person is immersed in water up to the neck, the hydrostatic force of the water moves extravascular fluid into the vascular space. Normal adaptations during pregnancy that maintain adequate uteroplacental blood flow include an early increase in plasma volume, higher cardiac output, and lowered systemic vascular resistance. In pregnant women with preeclampsia or intrauterine growth restriction, these adaptations fail or are inadequate, and immersion is a possible strategy for correcting the situation. Conceivably, the resultant intravascular volume expansion would improve hemodynamic function in the same way as intravenous hydration and thereby enhance uteroplacental blood flow.The effects of 35 minutes of water immersion were examined in 19 healthy, pregnant, nulliparous women at 26 to 29 and 34 to 37 weeks’ gestation. None of the women had a diastolic blood pressure greater than 90 mm Hg or a prepregnancy body mass index exceeding 30 kg/m; all women delivered a healthy term infant. Using a randomized crossover design, the women were immersed or rested in bed in a recumbent position for the same period, and treatments were alternated a week later. Blood pressure was recorded by an ambulatory monitor, and thoracic electrical bioimpedance was monitored noninvasively using a cardiac output monitor. Mean arterial pressure fell from 84 to 76 mm Hg during immersion at 26 to 29 weeks and from 89 to 80 mm Hg at 34 to 37 weeks, returning to preimmersion levels within 90 minutes. Impedance measurements obtained at 26 to 29 weeks demonstrated no significant difference in cardiac output between women who were immersed and those assigned to bed rest. Nevertheless, cardiac output was significantly higher immediately after immersion than in the bed rest group. Immediate postimmersion values exceeded output values recorded the next morning, indicating that the changes resulted from rest rather than immersion itself. No significant differences in stroke volume, systemic vascular resistance, or heart rate were observed between the immersion and bed rest groups. Immersion did not alter hemoglobin or hematocrit values, but thrombocytes were increased immediately afterward. Immersion increased urine production at both intervals, but there were no significant changes in 24-hour urine production or serum levels of creatinine, sodium, or potassium. Immersing pregnant women in water has clear but short-lasting effects on blood pressure, cardiac output, an