Buytaert 1983.

Methods	RCT, 2‐arm trial with individual randomisation.
Participants	45 non‐anaemic women with singleton pregnancy and no major illnesses attending the University Hospital Obstetric and Gynaecologic Clinic in Antwerp, Belgium.
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1: received 105 mg of elemental iron (as ferrous sulphate sustained release preparation) daily; group 2: received no iron supplement. Supplementation started at 14‐16th week of gestation and continued until delivery. Setting and health worker cadre: the intervention was performed by obstetricians at the University Hospital Obstetrical Clinic of the Erasmus University at Rotterdam, The Netherlands or the University Hospital Obstetric and Gynecologic Clinic in Antwerp, Belgium.
Outcomes	Maternal: Hb, serum iron, serum transferrin and serum ferritin concentrations at 16, 28, 36 weeks, delivery and 6 weeks postpartum.
Notes	Unsupervised. The randomisation was made for each clinic in Antwerp, and the results are presented separately by clinic. 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) (14th‐16th week). Anaemic status at start of supplementation: non‐anaemic. Daily iron dose: higher dose of iron (60 mg of elemental iron or more) (105 mg elemental iron). Iron release formulation: sustained release preparation. 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	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	Unclear risk	Management was altered depending on outcomes (women in the no treatment group who developed anaemia were treated).
Incomplete outcome data (attrition bias) All outcomes	Low risk	Less than 20% lost to follow‐up.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Unclear risk	No other bias apparent.