Mirghafourvand 2013.

Methods	Triple‐blind randomised controlled clinical trial.
Participants	126 pregnant women, aged 18 to 39 years with gestational age of 25 to 30 weeks referring to Tabriz health centres, Iran in 2013 to 2014.
Interventions	Participants were allocated to 3 groups using a randomised block design with block sizes of 3 and 6 with the allocation ratio 1:1:1: group 1 (n = 40) Calcium‐vitamin D group (300 mg carbonate calcium plus 1000 units of vitamin D supplements; group 2 (n = 42) vitamin D group (1000 units of vitamin D supplements; and group 3 (n = 42) received placebo. To hide the allocation, each participant received 2 small envelopes, each with enough medicine for 3 weeks, inside a large matte‐coloured envelope of the same shape that were serially numbered. Each participant received 1 pill every day for 42 days. All pills were of the same shape, size, and weight. Health worker cadre: not specified.
Outcomes	Maternal: gestational age, mode of delivery based on gestational age. food consumption, in terms of calcium and vitamin D content, pre‐pregnancy BMI, BMI during pregnancy Infant: weight, height, and head circumference, birthweight, height, head circumference. Laboratory method used for assessment of vitamin D concentrations: not specified.
Notes	Total dose of supplementary vitamin D during pregnancy: 56,000 to 200,000 IU; Start of supplementation: 25 weeks of pregnancy or more; Pre‐gestational BMI (kg/m2): most were overweight; Supplementation scheme/regimen: daily; Skin pigmentation based on Fitzpatrick skin tone chart (Fitzpatrick 1988): mixed/unknown; Latitude: north of the Tropic of Cancer; Season at the start of pregnancy: all year round. Source of funding: this study was funded by a research grant of Tabriz University of Medical Sciences (Project number: 388). Dates of the study and location: July 2013 to April 2014, Iran. Declarations of interest among primary researchers (or state where this information is not reported by the trial authors): no conflicts of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were allocated to 3 groups using a randomised block design with block sizes of 3 and 6 with the allocation ratio 1:1:1.
Allocation concealment (selection bias)	Unclear risk	To hide the allocation, each participant received 2 small envelopes, each with enough medicine for 3 weeks, inside a large matte‐coloured envelope of the same shape that were serially numbered. Each participant received 1 pill every day for 42 days. Pills were of the same shape, size, and weight. However, authors did not mention how this was concealed from study staff.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants were blinded to the study treatments.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The trial reported that it was double‐blinded but they did not specify if those performing the assessments were blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Losses to follow‐up were documented. No missing data and no participant was eliminated from the analysis.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Low risk	The study appears to be free of other sources of bias.