Nygaard 2008.

Methods	Double‐blind, parallel group RCT
Participants	45 pregnant women with rest cramps and no previous cramp treatment. Recruitment by pamphlets provided to pregnant Norwegian women undergoing 18 week ultrasound
Interventions	Either a chewable tablet containing 122 mg elemental magnesium ("primarily as Mg lactate and Mg citrate"), or a matched placebo tablet, taken once each morning and twice each evening for 2 weeks
Outcomes	Number of days or nights in which cramps occurred over 2 weeks. Degree of cramp pain on a 5‐point ordinal scale. Side effects. Serum magnesium and calcium and 24‐h urinary magnesium on days 1 and 15
Notes	Published. Source of funding not provided.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “The randomization program was provided by Medstat Research AS.” Comment: Probably adequate
Allocation concealment (selection bias)	Unclear risk	No description of allocation method given
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: “Both groups received a plastic container with the trial medication, 42 chewable tablets...”, containing either magnesium or placebo, both provided by the manufacturer Comment: Probably adequate
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	7/45 women (15.6%) dropped out (2 from the treatment arm and 5 from control). Reasons were given and most were unrelated to potential drug effects. None of the 7 were included in the analysis because of a lack of data.
Selective reporting (reporting bias)	Low risk	Primary outcome assumed to be the number of days and nights with cramping but not explicitly stated. All outcomes reported.
Cramp diary (recall bias)	Low risk	Diary used
Other bias	Unclear risk	Frequency of cramping at baseline was not assessed, making it impossible to tell if the group was imbalanced in this important baseline characteristic