Taherian 2002.

Methods	Randomised controlled study with 3 arms.
Participants	990 nulliparous women attending antenatal outpatient clinics of Isfahan Health Centers (32.6333° N, 51.6500° E north of Tropic of Cancer) between April 1998 and March 2001, with singleton pregnancies, first prenatal visit before 20 weeks of gestation, systolic/diastolic blood pressure lower than 130/80 mmHg, and no proteinuria detectable by a dipstick. Women with history of cardiovascular, renal or endocrinologic problems, medical or obstetric complications and those with known hazardous condition (multifetal gestation, hydatidiform mole) were excluded.
Interventions	Participants were randomly assigned to 1 of 3 groups: Group 1 (n = 330) received 75 mg aspirin each day from 20th week of gestation until delivery; Group 2 (n = 330) received a tablet containing 500 mg calcium carbonate + 200 IU vitamin D (cholecalciferol‐D3) daily from 20th week of gestation until delivery; and group 3 received no intervention (n = 330). All cases received standard prenatal care. Health worker cadre: the women were examined by trained staff every 4 weeks through the 28 weeks of gestation, and every 2 weeks through the 36th week and weekly thereafter. Blood pressure was measured by a certified examiner.
Outcomes	Maternal: blood pressure, bodyweight, BMI, maternal height, urine protein measurements, maternal weight gain, duration of gestation. Infant: neonatal weight at birth, the presence of respiratory distress syndrome, sepsis, jaundice and intrauterine growth retardation, fetal or neonatal death. Laboratory method used for assessment of vitamin D concentrations: not applicable.
Notes	Total dose of supplementary vitamin D during pregnancy: less than 56,000 IU; start of supplementation: 20 weeks of pregnancy or more; pre‐gestational BMI (kg/m2): normal weight (18.5 to 24.9); 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: April 1998 to March 2001. Source of funding: this study was funded by a research grant of the Research Deputy of Isfahan University of Medical Sciences grant (No: 76085). Dates of the study and location: April 1998 to March 2001, Iran. 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)	Low risk	Participants were randomised by table of random numbers.
Allocation concealment (selection bias)	Unclear risk	The trial did not report the methods for allocation concealment. It is unclear whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment. It is assumed that it was not conceal as one group did not receive any treatment.
Blinding of participants and personnel (performance bias) All outcomes	High risk	The trial did not mention if it was blinded. It is assumed that it was not blinded to participants as one group did not receive any treatment.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The trial did not mention if it was blinded to those conducting the assessments.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No attrition reported.
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 evident sources of bias.