Naghshineh 2016.

Methods	Double‐blind randomised controlled trial.
Participants	140 nulliparous pregnant women who had been referred to “Shahid Beheshti” hospital in Isfahan, Iran. Pregnant women at less than 16 weeks' gestation from outpatient clinics at “Shahid Beheshti” hospital were eligible if they did not have any sign of vitamin D deficiency, did not using aspirin and had no diagnosis of chronic hypertension, gestational diabetes, renal disease or systemic lupus erythematous.
Interventions	Subjects were randomly divided into 2 groups: Group 1 (n = 70) received supplementation with 600 IU daily of vitamin D at 16 weeks' gestation until labour; Group 2 (n = 70) received daily supplementation free of vitamin D and followed until labour (placebo group). Women were unaware of the treatment allocation. Health worker cadre: women were followed up monthly by a doctor who was blinded to the study groups.
Outcomes	Maternal: age and gestational age at delivery, pre‐eclampsia Infant: birthweight Laboratory method used for assessment of vitamin D concentrations: not applicable.
Notes	Total dose of supplementary vitamin D during pregnancy: 56,000 IU or less; start of supplementation: less than 20 weeks of pregnancy; pre‐gestational BMI (kg/m2): unknown/mixed; 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: From May 2012 until January 2012. Source of funding: this study was funded by a research grant. Financial support was provided by the Isfahan University of Medical Sciences (Grant 392004); Isfahan, Iran. Dates of the study and location: May 2012 to January 2012, Iran. Declarations of interest among primary researchers (or state where this information is not reported by the trial authors): none declared.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Using random‐maker software “Random Allocation”, participants were randomly divided into 2 groups: intervention and placebo.
Allocation concealment (selection bias)	Unclear risk	Women were unaware of the treatment allocation but no other information was provided.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Research staff was unaware of the treatment allocation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Follow‐up visits was done by blinded study personnel.
Incomplete outcome data (attrition bias) All outcomes	Low risk	2 participants for the intervention group were missing, but it was explained in the results section that they did not want to continue in the study. Total of 138 participants (68 cases and 70 controls) were analysed and described
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.