Roth 2010.

Methods	Randomised placebo‐controlled trial (AViDD‐2 trial)
Participants	160 pregnant women aged 18 < 35 years old, attending to the International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh (latitude: 23.7000° N, 90.3750° E, north of the Tropic of Cancer). Inclusion criteria: women with residence in Dhaka, with plans to have the delivery performed at the Shimantik maternity centre, and to stay in Dhaka throughout the pregnancy and 1 month past the delivery, with gestational age of 26th to 29th (inclusive), estimated based on the first day of the last menstrual period. Exclusion criteria: use of any dietary supplement containing more than 400 IU/day (10 mcg/day) of vitamin D within the month prior to enrolment, or refusal to stop taking supplemental vitamin D at any dose after enrolment, current use of anti‐convulsant or anti‐mycobacterial (tuberculosis) medications, severe anaemia (haemoglobin concentration < 70 g/L), complicated medical or obstetric history: cardiovascular disease, uterine haemorrhage, placenta praevia, threatened abortion, hypertension, pre‐eclampsia, preterm labour, or multiple gestation), prior history of delivery of an infant with a major congenital anomaly, birth asphyxia, or perinatal death (stillbirth or death within first week of life).
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1 (n = 80): women received vitamin D (cholecalciferol‐D3) 35,000 IU per week, started at 26 to 29 weeks' gestation, until delivery; group 2 (n = 80): women received placebo control administered weekly from 26 to 29 weeks' gestation until delivery. Health worker cadre: supplement doses were measured in disposable plastic syringes and orally administered by study personnel.
Outcomes	Maternal: serum 25‐hydroxyvitamin D concentration, serum calcium concentration, urine Ca:Cr ratio. Infant: immune function, infant growth, postnatal vitamin D status, serum calcium. Laboratory method used for assessment of vitamin D concentrations: Serum 25‐hydroxyvitamin D was quantified by high‐performance liquid chromatography tandem mass spectroscopy (LCMS/MS) in the Department of Pathology and Laboratory Medicine at the Hospital for Sick Children.
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): 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: summer. Source of funding: this study was funded by a Non‐governmental organization (NGO). The Thrasher Research Fund, Salt Lake City, USA. Dates of the study and location: August 2010 to January 2011, Dhaka, Bangladesh. Declarations of interest among primary researchers (or state where this information is not reported by the trial authors): the authors declare that they have no competing interests.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Trial reported computer‐generated randomisation list for the randomisation procedures.
Allocation concealment (selection bias)	Low risk	The allocation sequence was prepared by International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh personnel not otherwise involved in the study, and was concealed from investigators.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Trial reported that participants were blinded to allocation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Trial reported that research staff (including lab personnel) were blinded to allocation.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Of the 160 participants recruited and randomly assigned to intervention or placebo, 13 were lost to follow‐up prior to delivery (6 in the placebo group and 7 in the vitamin D group), all because of having left the Dhaka area.
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.