(Patho)physiological implications of chronic dietary sodium restriction during pregnancy; a longitudinal prospective randomized study. Preferred salt levels and salt taste acuity in human subjects after ingestion of untasted salt. Low sodium diet and pregnancy-induced hypertension: a multi-centre randomised controlled trial. Divergent hemodynamic and hormonal responses to varying salt intake in normotensive subjects. Randomized investigation of magnesium sulfate for prevention of preterm birth. Randomised controlled trial of effect of fish-oil supplementation on pregnancy duration. Exercise tolerance in the heat on low and normal salt intakes. Hyponatraemia and non-electrolyte solutions in labouring primigravida. Are asthmatics salt-sensitive? A preliminary controlled study.
To study the possible pathophysiological implications of long continued dietary sodium restriction in pregnancy.
                Longitudinal prospective randomized study of the effects of a low sodium diet compared with unrestricted sodium intake in pregnancy.
                Academic Department of Obstetrics and Gynaecology at Sint Radboud Hospital, Nijmegen, The Netherlands.
                42 healthy nulliparous women.
                A low sodium diet (20 mmol sodium daily) started in the 14th week of pregnancy and stopped after delivery.
                Maternal weight gain, food intake, blood pressure, cardiac output, systemic vascular resistance, haematocrit and birthweight.
                Total maternal weight gain and dietary energy intake during pregnancy and weight at 1 and 6 weeks postpartum were significantly lower in the low sodium group. Blood pressure during pregnancy did not show major differences. Stroke volume and cardiac output during pregnancy were significantly lower in the low sodium group whereas systemic vascular resistance was significantly higher. Haematocrit values in the low sodium group tended to be lower during pregnancy, but were significantly lower at 1 and 6 weeks postpartum than in the unrestricted group. Placental and birthweights were not significantly different between the two groups.
                Chronic dietary sodium restriction during pregnancy is characterized by a diminished body fat accumulation and a reduction in circulating volume, due to a decrease in both plasma and red cell volume, in combination with a high systemic vascular resistance without major effects on blood pressure and birthweight. We have examined whether salt loading alters the salt preference or salt taste acuity of nine human subjects on continuous low salt diet. Subjects were randomly assigned to either untasted salt tablets (120 mmol/day) or placebo over a 2-week period at the end of which salt preference and salt recognition thresholds were measured. Subjects then received the alternate substance for another 2 weeks and the measurements were repeated. While urinary Na+ and Cl- were significantly increased while on salt tablets, urinary volume, K+, urea and creatinine concentrations, blood pressure, body weight, salivary and plasma electrolyte concentrations were unchanged. Plasma renin and aldosterone levels were reduced while on salt tablets but not significantly. Salt tablets caused a significant increase in sodium recognition threshold but a significant decrease in salt addition to unsalted tomato juice and in ideal salt level assessed by presalted (150 mmol/l) tomato juice. Thus, an increase in untasted dietary salt may reduce salt preference in human subjects, a finding opposite to that with an increased, tasted salt intake over a similar period. 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.
                Multi-centre randomised controlled trial between April 1992 and April 1994.
                Seven practices of independent midwives and one university hospital.
                The experimental group comprised 184 women given a low sodium diet (< or = 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.
                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.
                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.
                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. Blood pressure responses to 1 week of low-salt (20 mmol sodium/d) and high-salt (300 mmol sodium/d) intake were investigated in a single-blind randomized study in 163 white, nonobese normotensive subjects (65 women and 98 men; mean age, 38 +/- 1.2 years). The individuals were classified as salt sensitive when mean arterial blood pressure rose by at least 5 mm Hg during high-salt intake, as salt resistant when mean arterial blood pressure changed by less than 5 mm Hg, and as "counterregulator" when mean arterial blood pressure fell by at least 5 mm Hg during the high-salt diet. Reexamination of 31 subjects showed that this approach to the testing of salt sensitivity was reliable and reproducible. Thirty subjects (18.4%) were classified as salt sensitive, 108 (66.3%) as salt resistant, and 25 (15.3%) as counterregulators. Multiple regression analysis revealed that age, body weight, and family history of hypertension contributed significantly to the change in blood pressure after the diets. Salt sensitivity was more frequent in older subjects and in those with a positive family history of hypertension. An increase in blood pressure after salt restriction was more likely in younger individuals and in those with a negative family history of hypertension. Plasma renin activity and plasma aldosterone concentrations were lower in salt-sensitive compared with salt-resistant and counterregulating subjects. The rise in plasma renin activity during salt restriction was most pronounced in counterregulating subjects. Plasma norepinephrine concentrations were not different among the groups.(ABSTRACT TRUNCATED AT 250 WORDS) One hundred fifty-six women with preterm labor between 24 and 34 weeks' gestation were randomized to receive either intravenous magnesium sulfate or no tocolytic therapy. Magnesuim sulfate infusions of up to 3 gm/hr were used in 76 pregnancies and resulted in a mean serum magnesium concentration of 5.5 +/- 1.4 mEq/L (mean +/- SEM). Compared with 80 control pregnancies, magnesium sulfate tocolysis had no significant effect on duration of gestation, birth weight, neonatal morbidity, and perinatal mortality. We conclude that clinically safe infusions of magnesium sulfate are ineffective when used to prevent preterm birth. The high birthweights and long duration of pregnancy in the Faroe Islands led us to suggest that a high intake of marine-fat-derived n-3 fatty acids might prolong pregnancy by shifting the balance of production of prostaglandins involved in parturition. We have compared the effects on pregnancy duration, birthweight, and birth length of a fish-oil supplement, a control olive-oil supplement, and no supplementation. 533 healthy Danish women in week 30 of pregnancy were randomly assigned in a ratio of 2/1/1 to fish oil (four 1 g Pikasol capsules [containing 2.7 g n-3 fatty acids] per day), olive oil (four 1 g capsules per day), or no supplement. The three groups differed in mean length of gestation (p = 0.006), which was highest in the fish-oil group and lowest in the olive-oil group; the result was similar when the analysis was restricted to women with an estimate of gestation length based on early ultrasound findings (443 women). Pregnancies in the fish-oil group were on average 4.0 (95% confidence interval 1.5-6.4) days longer than those in the olive-oil group; the difference in birthweight was 107 (1-214) g. The effect of supplementation on length of gestation was influenced by intake of fish and of fish oil: the difference between fish-oil and other groups was increased by a low fish intake at baseline. Fish-oil supplementation in the third trimester seems to prolong pregnancy without detrimental effects on the growth of the fetus or on the course of labour. 1. Salt restriction is recommended in the treatment of hypertension and is included in national dietary guidelines, but its effect on exercise in hot conditions has not been extensively studied. 2. The effects of 2 weeks on two levels of salt intake (50 and 150 mmol/day) on the ability to exercise (60% of maximal oxygen uptake) in a hot environment (35 degrees C) were studied in eight healthy normotensive subjects. 3. All subjects were able to complete the exercise load on the two levels of salt intake. No differences in mean oxygen uptake, heart rate or rectal temperature during exercise were observed between the two salt intakes. 4. Plasma sodium, potassium and osmolality were similar on the two salt intakes both before and during exercise. Plasma renin activity and aldosterone concentration were elevated after 2 weeks on the reduced salt intake and remained so during exercise. 5. The estimated sweat rate during exercise was similar on the two salt intakes but the loss of sodium was less on the low salt intake. 6. On the basis of these results it is concluded that moderate salt restriction does not impair the ability to exercise in a hot environment. We performed a prospective randomised study on one hundred primigravid women who required oxytocin to augment labour, comparing dextrose infusion with normal saline. After delivery, the 45 patients whose oxytocin was infused in dextrose had significantly lower serum sodium levels in both mother and baby compared to the 48 patients who had their oxytocin administered in normal saline. This was particularly evident in those cases where epidural analgesia was employed. Epidemiologic evidence suggests that high levels of salt consumption are associated with "spastic" disorders of smooth muscles, ie, essential hypertension and bronchial asthma. Experimentally, it has been shown that high intake of salt leads to increased bronchial hyperreactivity in asthmatics, ie, enhanced contractility of bronchial muscle to spasmogenic stimuli. On the basis of these observations, the following questions were asked: (1) Does salt loading worsen the clinical and functional findings in asthmatics? (2) Is it the sodium or the chloride in salt that is important?
                To answer these questions, the effect of salt restriction (= 5 to 6 g NaCl/d = 86 to 103 mmol Na), salt loading (+ 6.1 +/- 2.8 g NaCl/d = + 105 +/- 48 mmol Na), and loading with sodium citrate in nearly equimolar concentrations (+ 140 +/- 40 ml Shohl's solution, = + 120 +/- 30 mmol Na) was investigated in 14 asthmatics in a controlled crossover study. The total sodium load during the high salt diet was 191 to 209 mmol of sodium per day and during the sodium-citrate phase, 206 to 223 mmol of sodium per day.
                Statistical analysis showed that salt loading worsened symptoms (p = 0.06) and increased the use of inhaled steroids (p < 0.05). The effect on lung function was less equivocal: salt loading worsened the forced expiratory volume in 1 s (p < 0.01) and the peak expiratory flow rate (p < 0.05). This effect was presumably mediated by sodium, not chloride, as is demonstrated by loading with sodium citrate.
                Patients with bronchial asthma seems to be salt-sensitive, the responsible ion being presumably sodium. A low-salt diet appears to have a favorable effect in patients with asthma and to reduce the need for anti-asthma drugs.
Salt consumption during pregnancy should remain a matter of personal preference.