Effects of diuretics on plasma volume in pregnancies with long-term hypertension

The purpose of this randomized, prospective study was to investigate the effects of diuretics on plasma volume findings and perinatal outcome in pregnancies complicated by mild long-term hypertension. Twenty patients were in their first trimester and were receiving diuretics at time of entry to the study: Ten patients were allowed to continue their diuretic medication throughout pregnancy (diuretic group), whereas for the other 10 patients, diuretics were discontinued immediately. Plasma volume was serially measured throughout pregnancy with the use of the Evans blue dye-dilution technique. Initial plasma volume was similar in the two groups. However, in the diuretic group, subsequent plasma volume findings at various stages of gestation were markedly reduced when compared to respective plasma volume findings in the other group. In addition, plasma volume expansion was minimal in the diuretic group (mean increase of 18%), whereas it was normal in the other group (mean increase of 52%). Two patients in the diuretic group and one patient in the other group required other antihypertensive medication. There was no difference in perinatal outcome between the two groups. These results suggest that in hypertensive pregnancies, diuretics prevent normal plasma volume expansion without influencing perinatal outcome.