Characteristics of included studies [ordered by study ID]
Netherlands 1997
|
| Methods | Randomisation: 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. |
|
| | Participants | 270 nulliparous women with a singleton pregnancy after 12 weeks, by dates and ultrasound. Excluded if pre-existing HT, diabetes, renal disease, cardiovascular disease. |
|
| | Interventions | Low: 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. |
|
| | Outcomes | Woman: 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. |
|
| | Notes | Two 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 |
| | Bias | Authors' judgement | Support for judgement |
| | Allocation concealment? | Unclear risk | B - Unclear |
|
|
Netherlands 1998
|
| Methods | Randomisation: 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. |
|
| | Participants | 361 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. |
|
| | Interventions | Low: sodium-restricted diet, aimed at less than 50 mmol/day. Written dietary instructions given by midwife.
Normal: asked not to change eating habits. |
|
| | Outcomes | Woman: 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. |
|
| | Notes | Multicentre 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 |
| | Bias | Authors' judgement | Support for judgement |
| | Allocation concealment? | Low risk | A - Adequate |
|
|
DBP: diastolic blood pressure
GH: gestational hypertension
HT: hypertension
hr: hour
NICU: neonatal intensive care unit
PE: pre-eclampsia
PIH: pregnancy induced hypertension
SGA: small-for-gestational age
Characteristics of excluded studies [ordered by study ID]
|
| Study | Reason for exclusion |
|---|
| | Australia 1986a | No 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 1986b | No 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 1986 | No 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 1958 | Not 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 1961 | Not 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 1961 | No 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. |
|
|
APH: antepartum haemorrhage
PPH: postpartum haemorrhage
Comparison 1. Low versus normal salt intake in pregnancy
|
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
|---|
| | 1 Gestational hypertension | 1 | 242 | Risk Ratio (M-H, Fixed, 95% CI) | 0.98 [0.49, 1.94] |
| | 2 Pre-eclampsia | 2 | 603 | Risk Ratio (M-H, Fixed, 95% CI) | 1.11 [0.46, 2.66] |
| | 3 Visit to day care unit | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 1.05 [0.48, 2.32] |
| | 4 Antenatal hospital admission | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 0.82 [0.56, 1.22] |
| | 5 Placental abruption | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 0.19 [0.01, 3.98] |
| | 6 Caesarean section | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 0.75 [0.44, 1.27] |
| | 7 Perinatal death | 2 | 409 | Risk Ratio (M-H, Fixed, 95% CI) | 1.92 [0.18, 21.03] |
| | 8 Small-for-gestational age | 1 | 242 | Risk Ratio (M-H, Fixed, 95% CI) | 1.5 [0.73, 3.07] |
| | 9 Preterm birth | 1 | 242 | Risk Ratio (M-H, Fixed, 95% CI) | 1.08 [0.46, 2.56] |
| | 10 Apgar score <7 at 5 minutes | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 1.37 [0.53, 3.53] |
| | 11 Admission to neonatal intensive care unit | 1 | 361 | Risk Ratio (M-H, Fixed, 95% CI) | 0.98 [0.69, 1.40] |
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