Does oral magnesium substitution relieve pregnancy-induced leg cramps?

Our aim was to assess the effect of 360mg magnesium oral substitution daily among pregnant women suffering from leg cramps in pregnancy, defined as painful cramps different from restless legs symptoms.

In a double blind randomised controlled trial healthy pregnant women between 18 and 36 weeks of pregnancy suffering from painful leg cramps, at least twice a week, were invited to participate. Forty-five women were enrolled initially, 38 completed the treatment and were treated during 2 weeks with either magnesium (360mg=15mmol magnesium lactate and magnesium citrate, Nycoplus Magnesium), or placebo tablets. Serum magnesium and calcium were investigated together with urine magnesium and magnesium-creatinin ratio on day 1 and day 15. Frequency and intensity of leg cramps were recorded. The study was powered to detect a 50% reduction in leg cramps.

Registration of pain frequency and intensity during the two study weeks demonstrated no significant differences between the two groups. Mean number and intensity of cramps were 9.5 (S.D. 5.1) and 13.2 (S.D. 6.5) in the magnesium group, compared to 7.7 (S.D. 4.7) and 11.4 (S.D. 8.5) in the placebo group. Baseline magnesium levels were 0.77 and 0.74mmol/L in the magnesium group and the placebo group, respectively No significant differences between the two groups, or within the groups, were found when comparing serum values of serum magnesium and total calcium at inclusion time and at the end of the treatment. There was a statistically significant increase in magnesium excretion in the magnesium treatment group (p<0.01). The number of dropouts was two in the treatment group and five in the control group.

No significant effect on frequency or intensity of leg cramps in pregnant women of magnesium treatment with 360mg daily could be detected in this trial.