Shakiba 2013.

Methods	Randomised clinical trial
Participants	Healthy, pregnant women from the beginning of their second trimester of pregnancy. Exclusion criteria were not explicitly stated.
Interventions	Group A (n = 17): 50,000 IU/month. Group B (n = 17): 100,000 IU/month (50,000 IU every 2 weeks). Group C (n = 17): vitamin D deficient women (25(OH)D levels < 20 ng/mL) were treated with a total of 200,000 IU (50,000 IU/week for 4 weeks), followed by supplementation with 50,000 IU/month. Health worker cadre: the women were randomly recruited from 2 primary care clinics, a locality known to have a high prevalence of vitamin D deficiency, in Yazd (31°53’50”N/54°22’04”E), Iran (north of tropics), where > 90% of the days are sunny. Obstetricians and midwives conducted monthly visits to ensure that the participants adhered to the recommended dosage of vitamin D3. A paediatrician examined the neonate for possible anomalies and recorded the anthropometric measurements at the time of delivery. Other health workers not mentioned.
Outcomes	Maternal Secondary Serum 25(OH)D at term Infant Primary Preterm birth Secondary (infant) (25(OH)D) in cord blood Birthweight Birth length Laboratory method used for assessment of vitamin D concentrations: Chemiluminescence immunoassays (DiaSorin, spA, Via Crescentino, Vercelli, Italy)
Notes	• Start of supplementation: second trimester • Pre‐gestational BMI (kg/m2): unknown/mixed; • Supplementation scheme/regimen: weekly/monthly • Skin pigmentation based on Fitzpatrick skin tone chart (Fitzpatrick 1988): not available • Latitude: north of Tropics • Season at the start of pregnancy: autumn and winter of 2009 Source of funding: not reported. Dates of the study: not described. Declarations of interest among primary researchers: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient information about the sequence generation. Of the 51 participants, 34 were randomly classified into 2 groups (Groups A and B) and the remaining 17 women, were allocated to Group C based on their serum 25(OH)D levels
Allocation concealment (selection bias)	Unclear risk	Insufficient information to allow judgement.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Blinding was not reported in the study.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Blinding was not reported in the study.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing outcome data.
Selective reporting (reporting bias)	Low risk	The study protocol is not available but it is clear that the published reports include all mentioned outcomes (methods), including those that were pre‐specified.
Other bias	Unclear risk	Insufficient information to allow judgement.