Singh 2015.

Methods	Randomised controlled trial
Participants	100 healthy, pregnant women, primigravida with a singleton pregnancy, gestational age: 12‐16 weeks in Sawangi, Meghe, Wardha.
Interventions	Participants were randomised into 2 groups: Group 1 (n = 50): received 2000 IU of vitamin D3 per day from 12‐16 weeks of gestation of pregnancy; and Group 2 (n = 50) received no supplementation and served as controls. 25‐hydroxyvitamin D [25(OH)D]in maternal blood was measured by chemiluminescence immunoassay, at recruitment and at the time of delivery and a serum 25(OH)D level lower than30 nmol/L was defined as deficiency. Health worker cadre: not specified.
Outcomes	Maternal: deficiency of vitamin D, mean gestational age, preterm birth. Laboratory method used for assessment of vitamin D concentrations: Mean serum 25(OH)D levels were measured by Roche diagnostic ELECSYS (Electrochemiluminescence immunoassay) 2010 Cobase E 411 Analyser Immunoassay System Germany.
Notes	Total dose of supplementary vitamin D during pregnancy: 56,000 IU; start of supplementation: 12 to 16 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: all year, from October 2012‐September 2014. Source of funding: no funding sources reported. Dates of the study and location: October 2012 to September 2014, India. 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)	Unclear risk	The trial reported that participants were randomly allocated to the treatment or no supplementation but methods describing this process were not reported.
Allocation concealment (selection bias)	Unclear risk	The trial did not report this; however, since one group did not receive any supplementation, it is assumed that the intervention was not concealed to participants.
Blinding of participants and personnel (performance bias) All outcomes	High risk	The trial did not report this; however, it is assumed that participants were not blinded as one group did not receive any supplementation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The trial did not report if study staff was blinded.
Incomplete outcome data (attrition bias) All outcomes	High risk	It is assumed that each group had 50 participants as stated in the abstract but the trial did not report final number of participants that completed the trial or the sample size in any of the tables.
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.