Wallenburg 1983.

Methods	RCT, 2 arms with individual randomisation.
Participants	44 non‐anaemic Caucasian women with singleton pregnancy and no major illnesses attending the University Hospital Obstetrical Clinic of the Erasmus University in Rotterdam who had not received iron supplementation during their first visit.
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1: received 105 mg of elemental iron (as ferrous sulphate) daily in a sustained release preparation; group 2: received no iron supplement. Supplementation started at 14‐16th week of gestation until delivery. Setting and health worker cadre: the intervention was performed by physicians at the Antenatal Clinic of the University Hospital Dijkzigt in Rotterdam, the Netherlands.
Outcomes	Maternal: Hb, serum iron, serum transferrin and serum ferritin concentrations at 16, 28, 36 weeks, delivery, 6 and 12 weeks postpartum.
Notes	Unsupervised. Compliance not reported. We treated this study carried out collaboratively in 2 different sites as 2 different trials, 1 conducted in Rotterdam (Wallenburg 1983) and 1 conducted in Antwerp (Buytaert 1983). Gestational age at start of supplementation: early gestational age (supplementation started before 20 weeks' gestation). Anaemic status at start of supplementation: non‐anaemic. Daily iron dose: higher daily dose (more than 60 mg elemental iron daily). Iron release formulation: normal release preparation/unspecified. Iron compound: ferrous sulphate. 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	By random table numbers.
Allocation concealment (selection bias)	Low risk	By means of sealed envelopes.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participant nor provider blinded. No placebo used.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Low risk for laboratory outcomes.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Less than 20% losses to follow‐up.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Unclear risk	No other bias apparent.