Barton 1994.

Methods	RCT, 2‐arm trial with individual randomisation.
Participants	97 healthy women attending prenatal care at National Maternity Hospital, Dublin, Ireland with singleton pregnancy, during their first trimester of pregnancy, and with Hb equal or higher than 140 g/L were assigned to the groups. Women were excluded if they had a recent blood transfusion, chronic respiratory disease, chronic hypertension, renal disease, diabetes mellitus, history of haematologic disorder and alcohol dependence.
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1: received 60 mg elemental iron and 500 μg (0.5 mg) of folic acid to be taken by mouth twice daily; group 2: placebo tablets also to be taken by mouth twice daily. Supplementation started at 12 weeks until delivery. No postpartum supplementation. Setting and health worker cadre: the intervention was performed by physicians at the National Maternity Hospitalin Dublin, Ireland.
Outcomes	Maternal: Hb, HCT, serum erythropoietin concentrations at baseline and at 24, 28, 32, 36 and 40 weeks; serum ferritin at baseline and at 36 weeks; number of hypertensive disorders, antepartum haemorrhage, caesarean delivery. Infant: perinatal death, birthweight below 10th percentile, Apgar score, need for neonatal resuscitation and admission to neonatal intensive care unit data recorded but not reported in paper. Cord blood values of Hb, HCT, serum ferritin, and erythropoietin concentrations.
Notes	Unsupervised. No participants were withdrawn because of anaemia. Compliance not reported. Gestational age at start of supplementation: early gestational age (supplementation started before 20 weeks of gestation) (12 weeks until delivery). Anaemic status at start of supplementation: non‐anaemic. Daily iron dose: higher daily dose (60 mg elemental iron or more) (120 mg elemental iron). Iron release formulation: normal release/not specified. Iron compound: not specified. Malaria setting: non‐malarial setting. As of 2011: Malaria: no risk.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random numbers.
Allocation concealment (selection bias)	Unclear risk	Insufficient information reported on the method used to conceal the allocation sequence.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Reported as double blind. The placebo tablets were identical in size, colour and shape to the iron and folic acid supplements and contained the same excipients.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	It was not clear whether those assessing outcomes were aware of allocation, but it is unlikely that this possible lack of blinding affected the laboratory outcomes reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Less than 5% lost to follow‐up.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Low risk	No baseline imbalance apparent.