Low sodium diet and pregnancy-induced hypertension: a multi-centre randomised controlled trial

Objective To examine the effectiveness of the standard policy in the Netherlands to prescribe a sodium restricted diet to prevent or to treat mild pregnancy-induced hypertension. Design Multi-centre randomised controlled trial between April 1992 and April 1994. Setting Seven practices of independent midwives and one university hospital. Participants The experimental group comprised 184 women given a low sodium diet (less than or equal to 50 mmol sodium/day) and a control group of 177 women given a normal diet. Eligible women for inclusion had had a rise of blood pressure, or excessive weight gain or oedema during the antenatal period. The 361 women in the trial were recruited from 2020 nulliparae, of whom 1512 (75%) gave informed consent at the beginning of their pregnancy to participate in the study. Main outcome measures The difference between highest diastolic blood pressure after randomisation and diastolic blood pressure at the moment of randomisation; referral and admission to hospital for hypertension. Results There was no difference in increase of diastolic blood pressure after randomisation, the percentage of referral and admission to hospital for hypertension, or in obstetric outcome between the two groups. Urinary sodium excretion after randomisation in the normal diet group was significantly higher than in the low sodium group. Conclusion Prescribing a sodium-restricted diet to prevent or to treat mild pregnancy-induced hypertension is not effective. Therefore there is no need to introduce a salt restricted diet in prenatal care, although increasing evidence shows that a low sodium diet prevents hypertension in non pregnant individuals.