Soheilykhah 2011.

Methods	Randomised controlled trial
Participants	Pregnant women with GA less than 12 weeks without gestational diabetes, history of PCO, BMI less than 30 kg/m2 before pregnancy, no vitamin D supplementation in the past 6 months. Exclusion criteria: women with diabetes or gestational diabetes, treated with insulin, women with thyroid or parathyroid disorders, polycystic ovary disease before pregnancy, pre‐pregnancy BMI > 30 kg/m2, and, women who received vitamin D supplementation during the prior 6 months.
Interventions	Group B: 50,000 IU monthly (2000 IU daily) Group C: 50,000 IU every 2 weeks (4000 IU daily). Health worker cadre: the study was conducted in 2 prenatal clinics: Mojibian Hospital and Shahid Sadoughi Hospital) in Yazd, Iran. Latitude: 31.89 north of Tropics. Pregnant women were followed up every month during pregnancy and were evaluated regarding adverse effects of vitamin D. A blood sample for measurement of FBS, insulin, vitamin D and calcium was taken at the end of pregnancy for each participant. Specific research staff roles were not described.
Outcomes	Maternal Primary Adverse effects of vitamin D, such as headache and vomiting. Secondary Serum 25‐hydroxyvitamin D concentration at term Fasting blood sugar Laboratory method used for assessment of vitamin D concentrations: vitamin D was analysed by chemiluminescence assay with an inter‐assay coefficient of variation (CV) of 2.7% and an intra assay CV of 3.2%.
Notes	• Start of supplementation: supplementation began in the 12th week of pregnancy • Pre‐gestational BMI (kg/m2): < 30 kg/m2 • Supplementation scheme/regimen: biweekly and monthly • Skin pigmentation based on Fitzpatrick skin tone chart (Fitzpatrick 1988): not available • Latitude: north of Tropics • Season at the start of pregnancy: not stated Source of funding: none disclosed. Dates of the study: 2009‐2011. Declarations of interest among primary researchers: the authors report no conflicts of interest.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The participants were divided into 3 groups randomly. Computer‐generated random number lists were drawn up by an independent researcher.
Allocation concealment (selection bias)	Unclear risk	Insufficient information to allow judgment.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Pregnant women and researchers were not blinded to treatment assignment.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Pregnant women and researchers were not blinded to treatment assignment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	40 participants from group C, 38 cases from group B and 35 pregnant women from group A completed participation. Reasons for attrition were not mentioned, but group characteristics remained similar.
Selective reporting (reporting bias)	High risk	Authors reported that supplementation with 50,000 IU vitamin D every 2 weeks resulted in no adverse effects, such as hypercalcaemia, in pregnant women. Incidents of AE not reported for women in other intervention groups.
Other bias	Low risk	The study appears to be free of other sources of bias.