The role of plasma volume in hypertension in pregnancy (pre-eclampsla) was investigated. Significant volume expansion from non-pregnant levels (16·5±1·60 ml/cm height) was present throughout pregnancy in 189 normal women, reaching 23·1±1·21 ml/cm at 33–36 weeks amenorrhoea. In another 40 initially normotensive pregnant women who developed hypertension, simllar early volume expansion was followed by significant volume contraction in the third trimester, before elevation of blood pressure in 29 (20·6±1·26 ml/cm), after it in 11(18·6±1·27 ml/cm). Equivalent volume contraction was present in another 44 women studied only after hypertension developed in the third tri mester. Oedema had no value as a clinical sign.In another 30 women with chronic hypertension, blood pressure was inversely related to plasma volume (r=−0·822) and to fetal growth (r=−0·710), which was directly related to plasma volume (r=0·701). Plasma volume depletion plays a significant role in hyper
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