A Cochrane review [Abstract] 1 included 8 studies with a total of 576 pregnant women. Three studies compared magnesium with placebo, 1 compared calcium with no treatment, 1 compared calcium with placebo, and 1 compared calcium with vitamin C to treat leg cramps. One study was a four-arm RCT allocating women to receive calcium, magnesium, vitamin B or no treatment. One study was a three-arm RCT, in which women were allocated to receive vitamin D, calcium-vitamin D or placebo. Differences in outcome reporting precluded meta-analysis.
The results were inconsistent for frequency of leg cramps between oral magnesium and placebo/no treatment. Little or no differences in the occurrence of side effects (nausea, diarrhoea, flatulence and intestinal air) were found. The results were inconsistent also for other treatment compariosns.
An observational clinical trial 2 included 132 pregnant women with leg cramps in the first trimester of pregnancy. They were randomized 1:1 to 300 mg/day of oral Mg++ citrate (n = 66) or placebo (n = 66) for 4 weeks. There was a 28% (39/132) (CI 95%: 21 to 37) reduction of leg cramps in all participants and no difference between the two groups was found; reduction of 27% (18/66) (CI 95%: 17 to 40) in Mg++ group and 33% (21/66) (CI 95%: 22 to 46) in the placebo group. The OR of leg cramps was 1.3 (CI 95%: 0.6 to 2.9), p = 0.527, taking the placebo group as reference. Among pregnant women who remained with leg cramps the mean of leg cramps episodes per week showed no significance difference between the Mg++ and placebo groups; t-student test: p = 0.408.
Comment: The quality of evidence is downgraded by sparse data and study limitations.
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