Alterations in erythrocyte chloride content accompanying the changes in erythrocyte hydration and potassium content in normal human pregnancy: a comparison with pregnancy induced hypertension

Objectives To determine whether the change in erythrocyte potassium content in normal human pregnancy is accompanied by a similar change in erythrocyte chloride content. To assess erythrocyte hydration and potassium and chloride content in pregnancies complicated by proteinuric pregnancy induced hypertension. Design A serial study during and after normal pregnancy. A comparative study during and after pregnancies complicated by proteinuric pregnancy induced hypertension (PIH). Erythrocyte hydration, total osmoles, potassium and chloride and plasma osmolality were determined. Setting University teaching hospital, UK. Subjects Twenty‐eight women studied at 14, 28 and 36 weeks of normal pregnancy and ten women with PIH studied during the third trimester of pregnancy. All women were reinvestigated 20 weeks after delivery. Results The fall of erythrocyte potassium early in normal pregnancy (277.4 vs 265.2 mmol/kg; P <0.02) and its rise between 28 and 36 weeks (272.3 vs 288.0 mmol/kg; P <0.005) were accompanied by similar changes in erythrocyte chloride content (151.9 vs 131.1 mmol/kg; P <0.001 and 129.4 vs 141.3 mmol/kg; P <0.001, respectively). Plasma osmolality in PIH was raised above that normal in pregnancy (287.2 vs 283.0 mosm/kg; P <0.005). In PIH, compared to normal pregnancy, erythrocyte hydration (2.00 vs 1.89 l/kg dry weight cells), total osmoles (573.0 vs 534.2 mosm/kg), potassium (303.0 vs 288.0 mmol/kg) and chloride (154.9 vs 141.3 mmol/kg) were greater. Conclusions These findings further support the hypothesis that changes in plasma osmolality in pregnancy are secondary to alterations in cell osmoles and serve to limit changes in cell hydration. Erythrocyte composition and plasma osmolality are altered in PIH.