Tehrani 2014.

Methods	Single‐arm study, not blinded.
Participants	210 pregnant women referring to obstetric clinic of Shahid Beheshti and Alzahra hospital in Esfahan city in 2012. Inclusion criteria: patient satisfaction; normal BMI; gestational age below 16 weeks; no history of diabetes mellitus type 2 or GDM; no family history of diabetes mellitus type 1 in first degree relatives. Exclusion criteria: patient dissatisfaction; incorrect consumption of vitamin D supplementation; follow‐up discontinuation.
Interventions	Participants will be individually randomised to 1 of 2 groups: Group 1 (n = 70) received vitamin D supplementation with dose of 50,000 unit every 2 weeks for 10 weeks; Group 2 received a placebo. Pregnant women with levels of above 25 nmol/L were selected as the normal healthy control group and were the ones who received placebo. Health worker cadre: not specified.
Outcomes	Maternal: gestational blood sugar level, serum vitamin D level. Laboratory method used for assessment of vitamin D concentrations: not specified.
Notes	Total dose of supplementary vitamin D during pregnancy: more than 200,000 IU; start of supplementation: 20 weeks of pregnancy or more; pre‐gestational BMI (kg/m2): normal BMI; supplementation scheme/regimen: bi weekly; 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: unknown. Source of funding: this study was funded by a non‐governmental organization, Sponsor: Isfahan University of Medical Sciences. Dates of the study and location: January 2013 to January 2014, Iran. Declarations of interest among primary researchers (or state where this information is not reported by the trial authors): there are no conflicts of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were randomised by table of random numbers.
Allocation concealment (selection bias)	Low risk	Researcher, the distributors of the drug and the women, did not know which group was taken the vitamin D or placebo.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Researcher, the distributors of the drug and the women, did not know which group was taken the vitamin D or placebo.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Researcher, the distributors of the drug and the women, did not know which group was taken the vitamin D or placebo.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All data reported.
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 evident sources of bias.