Mazurkevich 2013.

Methods	Randomised control trial.
Participants	72 pregnant women with physiological pregnancy aged 18 to 35 years with low alimentary consumption of calcium (< 600 mg/day) who attended to Moscow State University of medicine and dentistry, department of obstetrics and gynaecology. (Latitude: 55.7500° N, 37.6167° E).
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1 (n = 43) received 1250 mg of calcium carbonate and 200 IU of vitamin D (cholecalciferol‐D3) from the second pregnancy trimester until term, in 2 takes a day; group 2 (n = 29) did not receive any treatment and served as controls. Health worker cadre: not specified.
Outcomes	Maternal: resistance of uterine arteries, resistance of umbilical arteries, uterine‐placental circulation. Infant: fetal‐placental circulation, intrauterine growth retardation, assessed by dopplerometry. 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 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: mixed/unknown. Source of funding: unknown/unreported. Dates of the study and location: not reported dates, Moscow, Russia. 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 intervention groups but they did not report the method of sequence generation.
Allocation concealment (selection bias)	Unclear risk	The trial did not report the method of concealment. It is assumed that they did not conceal the allocation as one of the groups did not receive any supplementation.
Blinding of participants and personnel (performance bias) All outcomes	High risk	The trial did not report if the study was blinded. It is assumed that it was not blinded to participants as one of the groups did not receive any supplementation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The trial did not report if research staff was blinded.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	There is insufficient information to permit judgement.
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.