Villar 1987.

Methods	Type of study: double‐blinded, randomised controlled clinical trial. Method of treatment allocation: the women were assigned randomly in the double‐blind fashion at 26 weeks' gestation to 1 of 2 treatment groups, using a randomisation schedule prepared in advance for the complete population. Stratification: not stated. Placebo: yes, starch tablets. Sample size calculation: not stated. Intention‐to‐treat analyses: yes. Losses to follow‐up: 0%.
Participants	Location: The Johns Hopkins Hospital in Baltimore and Perinatal Study Center of Rosario, Argentina. Time frame: 1983 to 1985. Eligible criteria: nulliparous, singleton, known LMP, age 18 to 30 years, free from any underlying medical disorders, negative roll‐over test. Exclusion criteria: history of cardiovascular or renal disease or taking any drug. Total recruited: 52 pregnant women: *18 white: 9 in calcium group, 9 in placebo group; *34 black women: 16 in calcium group, 18 in placebo group. Total in calcium group, n = 25; in placebo group, n = 27.
Interventions	3 tablets of calcium carbonate (500 mg each). Compared with 3 placebo tablets with same size, weight, size, colour and organoleptic characteristics. Started treatment at 26 weeks.
Outcomes	Incidence of PIH. Birthweight.
Notes	Comment: the authors provide only mean birthweight but not SD. SDs in both groups were imputed by mean.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The women were assigned randomly in the double blind fashion at 26 weeks gestation to one of two treatment groups, using a randomisation schedule prepared in advance for the complete population."
Allocation concealment (selection bias)	Low risk	Quote: "The same randomization code, standardization process, and tablets were used in both populations and code was kept in central allocation (Baltimore). Random number in closed envelopes and corresponding medication were distributing to the two hospitals at the beginning. All containers and tablets  were prepared by pharmaceutical."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "The women were assigned randomly in the double blind fashion at 26 weeks gestation to one of two treatment groups, using a randomisation schedule prepared in advance for the complete population." Quote: "Placebo same size, weight, size, colour and organoleptic characteristic."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "All BP value were measured by one nurse‐midwife and one physician especially recruited and trained for the study." Comment: not specifically stated that outcome assessors were blinded, but placebo and treatment were identical.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: all enrolled participants were included in the analyses. Missing data = 0%.
Selective reporting (reporting bias)	Low risk	None identified.
Other bias	Low risk	None identified.