Methods	Cluster-randomised trial.
Participants	484 apparently healthy pregnant women with 13-17 wks of gestation who had not received iron supplements before enrolling in the study, and who had a Hb concentration > 80 g/L attending antenatal care clinics at the district hospital and 7 health centres from 54 villages in the Province of Khon-Kaen in northeast Thailand
Interventions	The villages were grouped according to size and then randomised in 4 clusters to 1 of 3 interventions: group 1 received a daily regimen providing 60 mg of elemental iron (as ferrous sulphate) with 250 μg (0.25 mg) of folic acid daily; group 2 received 120 mg of elemental iron (as ferrous sulphate) with 3500 μg (3.5 mg) of folic acid once a week; and group 3 received 180 mg of elemental iron (as ferrous sulphate) with 3500 μg (3.5 mg) of folic acid once a week. Supplementation started at 15 +/− 2 wks until delivery. Setting and health worker cadre: the intervention was performed by lay health workers in rural villages in Ubolrat district of Khon-Kaen Province in Thailand
Outcomes	Maternal: Hb concentration, serum ferritin, free erythrocyte protoporphyrin at baseline and at 35 +/− 2 wks of gestation, and 4-6 months postpartum; haematocrit prior to delivery; weight at baseline and at 35 wks of gestation; compliance, Hb type, and hookworm prevalence. Infant: birthweight, Hb concentration and serum ferritin at 4-6 months
Notes	Unsupervised. Compliance not reported. Values adjusted to reflect effective sample size for cluster randomisation Gestational age at start of supplementation: early gestational age (supplementation started before 20 weeks’ gestation or prior to pregnancy) Anaemic status at start of supplementation: unspecified/mixed anaemia status at start of supplementation Dose of iron per week in intermittent group: (group 2) low weekly dose of iron in the weekly group (120 mg elemental iron or less per week) and (group 3) high weekly dose of iron in the weekly group (more than 120 mg elemental iron per week) Iron release formulation: normal release iron supplement/not specified; Iron compound: ferrous sulphate. Intermittent regimen: provision of iron once a week on non-consecutive days Malaria setting: study carried out in malaria risk locations.As of 2011: malaria risk exists throughout the year in rural, especially forested and hilly, areas of the whole country, mainly towards the international borders, including the southernmost provinces. There is no risk in cities (e.g. Bangkok, Chiang Mai city, Pattaya), Samui island and Phuket island.However, there is a risk in some other areas and islands
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Cluster-randomisation but method unclear.
Allocation concealment (selection bias)	High risk	Not used.
Blinding (performance bias and detection bias) All outcomes	High risk	Open.
Incomplete outcome data (attrition bias) All outcomes	High risk	More than 20% lost to follow-up. “… the analysis of data was performed only on women who ingested more than 75% of the iron tablets provided and whose haemoglobin never fell < 80 g/L”. 484 women randomised, 379 completed study (22% attrition). 11 excluded from the weekly group for poor compliance or because they received other supplements. Reasons for attrition across groups were not balanced
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 sources of bias.