Nygaard 2008.

Study characteristics
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") (n = 23), or a matched placebo tablet (n = 22), 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‐hour urinary magnesium on days 1 and 15
Conflicts of interest	1 author contributed in developing the magnesium tablet in 1985, and he received a compensation from Nycomed for this effort. The rest of the authors have no conflict of interest.
Funding	Source of funding not provided
Notes	Published. Conducted from August 2000 to January 2003
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “The randomization program was provided by Medstat Research AS.” Comment: probably adequate; however, the frequency of cramping at baseline was not assessed, making it impossible to tell if the group was imbalanced in this important baseline characteristic
Allocation concealment (selection bias)	Unclear risk	No description of any method of allocation concealment
Blinding of participants and personnel (performance 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
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcomes measured from forms completed by blinded participants
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 dropouts 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	Low risk	No other obvious bias