Taherian 2002.

Methods	Type of study: randomised controlled study. Method of treatment allocation: the sampling method was non probability convenience. Used table of random numbers to assign each case independently to 1 of 3 groups. Stratification: not stated. Placebo: no (no treatment). Sample size calculation: not stated. Intention‐to‐treat analyses: yes. Losses to follow‐up: 0%.
Participants	Location: Isfahan Health Centre, Iran. Time frame: April 1998 to March 2001. Eligible criteria: nulliparity, single gestation, first antenatal visit before 20 weeks of gestation, BP < 130/80 mmHg and no proteinuria by urine dipstick. Exclusion criteria: had history of cardiovascular, renal disease or endocrinologic problem, medical or obstetric complications and those with known hazardous condition (multiple gestation, hydatidiform mole). Total recruited: 990 healthy pregnant women (n = 330 participants/group).
Interventions	Group 1: received 75 mg aspirin /day, n = 330. Group 2: received 500 mg calcium carbonate/day, n = 330. Group 3: no treatment as control group, n = 330. Started treatment at 20 weeks until delivery.
Outcomes	BP. Pregnancy outcomes; GA, birthweight, preterm birth, Apgar score, fetal growth restriction, perinatal death.
Notes	Comment: the results were reported as mean and 95% CI; we changed them into SD.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The sampling method was non probability convenience. We used table of random numbers to assign each case independently to one of three groups."
Allocation concealment (selection bias)	Unclear risk	Comment: the method of allocation concealment was not stated.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "Group 1 received 75 mg aspirin; group 2 received 500 mg oral calcium‐D daily; and the control group 3 received no medication at all." Comment: it was impossible to blind because the difference between drug and no treatment in control group.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote:" All cases received prenatal care according to the approved model, BP, body weight and maternal height were measured." Comment: assessors were not blinded because the participants received different treatments.
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.