Supakatisant 2015.
| Study characteristics | ||
| Methods | Double‐blind, parallel‐group RCT | |
| Participants | 86 women with pregnancy induced rest cramps (mean 28.0 weeks' gestation) having at least 2 cramps per week and beng free of both medical disease and obstetrical complications. Recruitment was from a university‐affiliated antenatal specialty clinic in Thailand | |
| Interventions | Either magnesium bisglycinate chelate (100 mg elemental magnesium per tablet) (n = 43) or matched placebo tablet (n = 43), taken as 1 tablet 3 times daily with meals for 4 weeks. | |
| Outcomes | 50% reduction in cramp frequency (cramps per week) 50% reduction in cramp intensity VAS Side effects |
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| Conflicts of interest | Authors declare they have no conflict of interest. | |
| Funding | Independent funding | |
| Notes | Published. Conducted from June 2010 to August 2011 | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | A random number sequence with fixed blocks of 4 was generated from a random number table and used to number bottles of study medication, which were provided to participants in sequence as they were enrolled |
| Allocation concealment (selection bias) | Low risk | Nurses who were unaware of the contents of each bottle selected the next bottle in sequence and provided it to participants |
| Blinding of participants and personnel (performance bias) All outcomes | Low risk | "The opaque plastic container contained 84 tablets of magnesium or placebo (identical in size, shape and colour)." "Both health care providers and women were masked to treatment assignment." |
| Blinding of outcome assessment (detection bias) All outcomes | Low risk | Outcomes measured from diaries and forms completed by participants blind to treatment group |
| Incomplete outcome data (attrition bias) All outcomes | Unclear risk | 6/86 women did not complete the study (7%). In an ITT analysis, the authors treated these participants as "worst‐case scenario" but we confirmed this to mean that the trialists considered all participants with incomplete data as treatment failures. As 4 control group participants did not complete the study, and 2 intervention group participants did not complete the study, handling missing data in this way attributed 4 treatment failures to the control group and 2 to the intervention group. This approach biases the results in favour of the intervention (as compared to a more typical worst‐case scenario approach, which would conservatively categorize missing data in the intervention group as treatment failure but missing data in the control group as treatment success). |
| Selective reporting (reporting bias) | High risk | Primary outcome not clearly stated until the discussion (although the authors describe powering for what was eventually described as the primary outcome) and methods do not describe how each outcome was intended to be analysed. The reported results also appear incongruous despite requests for clarification from trial authors. In particular, the trial authors confirm that the median number of cramps per week increased from baseline in both groups (a median increase of 1 cramp per week in treatment and 3 cramps per week in control) while simultaneously reporting a large per cent reduction in cramp rates (a 79% reduction in the magnesium group and 32.4% reduction in the placebo group). A language barrier, mislabelling of results, or both, might explain some of these discrepancies. The reported median absolute change in pain score was also higher in the placebo group than in the treatment group. As the trial authors describe pain scores decreasing in both groups, this does not make sense and the trial authors probably mean this to be median pain on treatment rather than median absolute change. |
| Cramp diary (recall bias) | Unclear risk | Although the trial authors use the phrase "diary chart" in the text, it does not appear that individual cramps were recorded. Rather the "case record forms" that participants filled out appear to be based on recall of cramps at baseline and again upon conclusion of the study. |
| Other bias | Low risk | No obvious other bias |
CI: confidence interval ITT: intention‐to‐treat IV: intravenous Mg: magnesium RCT: randomized controlled trial VAS: visual analogue scale