Villar 1990.

Methods	Type of study: double‐blind, randomised placebo‐controlled clinical trial. Method of treatment allocation: computer‐generated list of random number. Opaque envelopes with the bottle number were located at the clinic and the project co‐ordinator was in charge of the administration of the treatment assigned. Stratification: not stated. Placebo: yes, starch tablets. Sample size calculation: not stated. Intention‐to‐treat analyses: yes. Losses to follow‐up: 0%.
Participants	Location: Adolescent Pregnancy Clinic of the Johns Hopkins Hospital in Baltimore. Time frame: 1985 to1988. Eligible criteria: age < 17 year, GA < 20 week, singleton pregnancy, certain LMP, free from any underlying medical disorders determined by history, physical examination, and laboratory tests. Exclusion criteria: underlying medical disorders determined by history, physical examination, and laboratory tests. Total recruited: 190 adolescent pregnant women; 95 in the calcium group, 95 in the placebo group.
Interventions	2 g of calcium (4 tablets of calcium carbonate per day, 500 mg of elemental calcium) compared with 4 tablets of placebo (contained lactose and granulated starch) per day, same size, weight and colour. Started treatment at 20 weeks until delivery.
Outcomes	Incidence of preterm labour. Incidence of low birthweight, IUGR, premature rupture of membrane, PIH. Pregnancy outcomes; GA, birthweight, birth length. Incidence of bacteriuria, pyelonephritis.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A computer‐ generated list  of random number was used to allocate the corresponding treatments."
Allocation concealment (selection bias)	Low risk	Quote: "Opaque envelope with the bottle number were locate at the clinic and project coordinator was in charge of the administration of the treatment assigned."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Treatment versus placebo. All participants were blinded to interventions. Placebo was the same size, weight, colour, and had the same organoleptic characteristics as the calcium tablets.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Placebo was he same size, weight, colour, and had the same organoleptic characteristics as the calcium tablets. The investigators were blinded to treatment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: all enrolled participants were analysed. Missing data = 0%.
Selective reporting (reporting bias)	Low risk	None identified.
Other bias	Low risk	None identified.