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To assess if hypertension during the last part of pregnancy could be prevented by magnesium supplementation.
Pregnant primagravida women from a local antenatal care unit were given an oral supply of 300 mg magnesium as citrate or placebo from pregnancy week 25 in a randomised double-blind setup. Blood pressure was recorded during pregnancy as well as pregnancy outcome.
In the magnesium-supplemented group, the average diastolic blood pressure at week 37 was significantly lower than in the placebo group (72/1.4 mean/SEM vs 77/1.4, p = 0.031). The number of women with an increase in diastolic blood pressure of ≥15 mmHg was significantly lower in the magnesium group compared with the women who received placebo (p = 0.011). There was an inverse relation between the urinary excretion of magnesium during pregnancy and the diastolic blood pressure (p = 0.005).
Magnesium supplementation prevented an increase in diastolic blood pressure during the last weeks of pregnancy. The relation between diastolic blood pressure and urinary excretion of magnesium suggests that magnesium is involved in the regulation of blood pressure and that the increase in diastolic blood pressure in pregnancy could be due to a lack of magnesium.