Li 2000a.

Methods	Clinical controlled trial with 3 arms.
Participants	88 pregnant women with a predisposition to pregnancy‐induced hypertension, at 20 to 24 weeks' gestation, a BMI index of lower than 24, and an arterial pressure of < 11.3 kPa attending an outpatient clinic and labour ward of the First Afilliated Hospital of Xi’an Medical University, Xi’an, China.
Interventions	Participants were divided into 3 groups: group 1 (n = 29) received a daily dose of a tablet containing 600 mg of calcium and 200 IU of vitamin D (Caltrate‐D) daily from 20 to 24 weeks until deliver; group 2 (n = 29) received 1200 mg of calcium and 400 IU vitamin D (Caltrate‐D) daily from 20 to 24 weeks until deliver; group 3 (n = 30) received no intervention from 20 to 24 weeks until delivery. Health worker cadre: not specified.
Outcomes	Maternal: blood pressure, ionised calcium and platelet intracellular calcium, incidence rates of pregnancy‐induced hypertension. Laboratory method used for assessment of vitamin D concentrations: not applicable.
Notes	Total dose of supplementary vitamin D during pregnancy: 56,000 IU vitamin D or less; 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 Tropic of Cancer; season at the start of pregnancy: all year round. Source of funding: unknown/unreported. Dates of the study and location: August 1996 to December 1998, China. 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)	High risk	The trial did not report if participants were randomly allocated to the treatment groups. It is unclear if it was random or not.
Allocation concealment (selection bias)	Unclear risk	The trial did not report the method of concealment. It is assumed that it was not conceal 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 it 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 mention if the study was single or double blinded.
Incomplete outcome data (attrition bias) All outcomes	High risk	Loss to follow‐up not reported.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to make a judgement.
Other bias	High risk	The report is very short, with most details of the methods not available.