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Altered dietary salt for preventing pre-eclampsia, and its complications

  1. Lelia Duley1,*,
  2. David J Henderson-Smart2,
  3. Shireen Meher3

Editorial Group: Cochrane Pregnancy and Childbirth Group

Published Online: 19 OCT 2005

Assessed as up-to-date: 23 JUN 2005

DOI: 10.1002/14651858.CD005548


How to Cite

Duley L, Henderson-Smart DJ, Meher S. Altered dietary salt for preventing pre-eclampsia, and its complications. Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD005548. DOI: 10.1002/14651858.CD005548.

Author Information

  1. 1

    University of Nottingham, Nottingham Clinical Trials Unit, Nottingham, UK

  2. 2

    Faculty of Medicine, University of Sydney, Central Clinical School, Sydney, NSW, Australia

  3. 3

    The University of Liverpool, Department of Women's and Children's Health, Liverpool, UK

*Lelia Duley, Nottingham Clinical Trials Unit, University of Nottingham, B39, Medical School, Queen's Medical Centre Campus, Nottingham, NG7 2UH, UK. lelia.duley@nottingham.ac.uk.

Publication History

  1. Publication Status: Edited (no change to conclusions)
  2. Published Online: 19 OCT 2005

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Characteristics of included studies [ordered by study ID]
Netherlands 1997

MethodsRandomisation: method not stated.
Allocation concealment: "closed envelope system", no further information.
Follow up: 28 women (10%) excluded. Low-salt 23 excluded: 17 refused diet, 3 social reasons, 2 medical reasons, 1 fetal trisomy. Normal-salt 5 excluded: 2 social reasons, 3 medical reasons grade (B).
Blinding: participants not blinded. Blinding of caregivers and outcome assessment not reported.


Participants270 nulliparous women with a singleton pregnancy after 12 weeks, by dates and ultrasound. Excluded if pre-existing HT, diabetes, renal disease, cardiovascular disease.


InterventionsLow: diet with about 20 mmol sodium per day. Oral and written instruction by dietician, no added salt and ready made foods only if no salt in preparation.
Normal: no dietary restriction.


OutcomesWoman: GH (DBP >/= 90 x 2 or >/= 110 x 1), PE (HT with proteinuria >/= 300 mg/24 hr), severe HT (DBP >/= 110)
Baby: death, SGA, preterm delivery.


NotesTwo centre study.
Setting: hospital clinics.
Mean urinary sodium after randomisation 70 mmol/day in the low sodium group, 135 mmol/day for normal diet.


Risk of bias

BiasAuthors' judgementSupport for judgement

Allocation concealment?Unclear riskB - Unclear

Netherlands 1998

MethodsRandomisation: random numbers in blocks of 10. Stratified by centre.
Allocation concealment: sealed, numbered, opaque envelopes.
Follow up: no loss to follow up (A).
Blinding: participants not blinded. Caregiver blinded only to urinary sodium concentration. Blinding of outcome assessment not reported.


Participants361 women booked for midwifery care, nulliparous, DBP < 90 mmHg at booking visit before 20 weeks. Randomised if DBP > 85 x 2 in subsequent visit, or weight gain > 1 kg/week for 3 consecutive weeks, or excess oedema. Excluded if planning to leave the city or risk factors for PIH.


InterventionsLow: sodium-restricted diet, aimed at less than 50 mmol/day. Written dietary instructions given by midwife.
Normal: asked not to change eating habits.


OutcomesWoman: highest DBP, PE (HT (not defined) with significant proteinuria (not defined)), eclampsia, hospital referrals and admissions for HT, time to delivery, abruption, mode of delivery.
Baby: death, gestation at delivery (mean), birthweight, Apgar at 5 minutes, NICU admission.


NotesMulticentre study: 9 centres.
Setting: midwifery practices and hospital clinic.
Mean urinary sodium after randomisation 84 mmol/day in low sodium group, 124 mmol/day for normal diet.


Risk of bias

BiasAuthors' judgementSupport for judgement

Allocation concealment?Low riskA - Adequate

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Australia 1986aNo clinical outcomes reported.

Study design: 'assigned randomly'.
Participants: 58 primigravid women.
Intervention: one week of either high-salt or low-salt diet.
Outcomes: plasma arginine vasopressin concentration, urinary sodium excretion.

Australia 1986bNo clinical outcomes reported.

Study design: 'assigned randomly'.
Participants: 40 primigravid women.
Intervention: one week of either high-salt or low-salt diet.
Outcomes: potassium excretion, sodium excretion, plasma progesterone, plasma aldosterone.

Belgium 1986No clinical outcomes reported in the abstract, and attempts to contact trialists revealed that the trial was stopped because the lead trialist left the institution. Attempts to contact the lead trialist were unsuccessful.

Study design: two groups were randomised and matched. No further information.
Participants: 30 pregnant women.
Intervention: 15 women followed a salt-poor diet and 15 women followed a salt-rich diet.
Outcomes: body fluid volume, vascular reactivity, clinical evolution, pregnancy outcome (but no data for these outcomes reported in the abstract).

UK 1958Not a randomised trial. Quasi-random, using alternate allocation of women attending clinic.

Study design: as above.
Participants: 2077 women at booking clinic, 58 excluded.
Intervention: high-salt diet with advice to add salt to diet and eat salty food versus low-salt with advice to avoid adding salt to food and not to eat salty food.
Outcomes: toxaemia, oedema, APH, PPH, caesarean section, breech delivery, forceps delivery, perinatal death, deformities, maternal side-effects.

UK 1961Not a randomised trial. Allocation by ward and by consultant. Participants were women with established pre-eclampsia.

Study design: as above.
Participants: 739 women with high blood pressure, oedema and proteinuria. Excluded if < 24 hours from admission to delivery.
Intervention: 2 g salt versus 10 g versus 25 g.
Outcomes: surgical induction, caesarean section, number of days in hospital, eclampsia, blood pressure trends, perinatal death, birthweight.

USA 1961No clinical outcomes reported.

Study design: 'assigned randomly'.
Participants: 58 primigravid women.
Intervention: one week of either high-salt or low-salt diet.
Outcomes: plasma arginine vasopressin concentration, urinary sodium excretion.

 
Comparison 1. Low versus normal salt intake in pregnancy

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Gestational hypertension1242Risk Ratio (M-H, Fixed, 95% CI)0.98 [0.49, 1.94]

 2 Pre-eclampsia2603Risk Ratio (M-H, Fixed, 95% CI)1.11 [0.46, 2.66]

 3 Visit to day care unit1361Risk Ratio (M-H, Fixed, 95% CI)1.05 [0.48, 2.32]

 4 Antenatal hospital admission1361Risk Ratio (M-H, Fixed, 95% CI)0.82 [0.56, 1.22]

 5 Placental abruption1361Risk Ratio (M-H, Fixed, 95% CI)0.19 [0.01, 3.98]

 6 Caesarean section1361Risk Ratio (M-H, Fixed, 95% CI)0.75 [0.44, 1.27]

 7 Perinatal death2409Risk Ratio (M-H, Fixed, 95% CI)1.92 [0.18, 21.03]

 8 Small-for-gestational age1242Risk Ratio (M-H, Fixed, 95% CI)1.5 [0.73, 3.07]

 9 Preterm birth1242Risk Ratio (M-H, Fixed, 95% CI)1.08 [0.46, 2.56]

 10 Apgar score <7 at 5 minutes1361Risk Ratio (M-H, Fixed, 95% CI)1.37 [0.53, 3.53]

 11 Admission to neonatal intensive care unit1361Risk Ratio (M-H, Fixed, 95% CI)0.98 [0.69, 1.40]