Hammar 1987.

Study characteristics
Methods	2‐arm randomised controlled trial, with 13 additional controls without leg cramps (not included in analysis).
Participants	Setting: Sweden. Inclusion criteria: pregnant women who had experienced leg cramps for more than 2 weeks. Exclusion criteria: not described
Interventions	Experimental intervention: oral calcium preparation containing calcium gluconate, calcium lactate and calcium carbonate corresponding to a calcium dose of 1 g twice daily for 3 weeks (30 women). Comparison intervention: vitamin C 1 g twice daily for 3 weeks (30 women).
Outcomes	Frequency of cramps, serum calcium, magnesium and albumin concentrations.
Notes	Dates of study: this information is not reported by the trial authors Funding sources: ACO Research Fund Declarations of interest: this information is not reported by the trial authors
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Study states that it was “randomised”, but there is no description of the method.
Allocation concealment (selection bias)	Low risk	Not specifically described, but the code was not broken until all women had completed the investigation, which suggests that allocation was concealed.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	The study was double‐blinded, and the code was not broken until all women had completed the investigation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The code was not broken until all women had completed the investigation.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All women appear to be accounted for in the analysis.
Selective reporting (reporting bias)	Unclear risk	Assessed from published report, without protocol. Focus is on biochemical outcomes, but all prespecified outcomes appear to be reported.
Other bias	Unclear risk	Insufficient information to assess whether another important risk of bias exists.