Chanarin 1965.

Methods	Randomised controlled trial with 3 arms.
Participants	190 pregnant women before 16 week of gestational age attending antenatal clinic for the first time in St Mary's Hospital in London, England, United Kingdom were invited to participate in the study and 189 accepted.
Interventions	Participants were randomly assigned to 1 of 3 groups: group 1 received 3 tablets containing 100 mg of ferrous fumarate to be taken daily (total 300 mg ferrous fumarate daily); group 2 received 3 tablets containing 100 mg of ferrous fumarate with 10 μg (0.01 mg) folic acid (total 300 mg ferrous fumarate and 30 μg (0.03 mg) folic acid daily; group 3 placebo (containing lactose). Setting and health worker cadre: the intervention was performed by obstetricians and pathologists at the antenatal clinic of St. Mary's Hospital in London, United Kingdom.
Outcomes	The outcomes measured include full blood count at 20th, 30th, 35th and 39th week of gestation and 6th day after delivery.
Notes	The paper does not report SDs in the variables measured and no data can be extracted. The trial is included but does not contribute data for the analysis. Gestational age at start of supplementation: early gestational age (supplementation started before 20 weeks' gestation). Anaemic status at start of supplementation: unspecified or mixed anaemia status. Daily iron dose: higher daily dose (60 mg of elemental iron or more). Iron release formulation: normal release preparation/unspecified. Iron compound: ferrous fumarate. 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)	Unclear risk	Methods not described.
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Partial blinding. This was a placebo‐controlled trial bottles containing medication were colour coded but it was stated that staff were not aware of the colour coding during the trial.
Blinding of outcome assessment (detection bias) All outcomes	High risk	It was stated that some women in the placebo group with anaemia were treated and withdrawn from the analysis for haematological outcomes; it was not clear whether staff were aware of allocation at the point of withdrawing these women. Excluding this section of the sample makes findings for the placebo group biased for these outcomes.
Incomplete outcome data (attrition bias) All outcomes	High risk	189 women were randomised but only 154 completed the study but not all samples could be obtained from every participant. 35 women were further withdrawn from the trial. 9 participants in the placebo group and 1 in the iron + folic acid group required parenteral iron nutrition and were withdrawn from the analysis.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Unclear risk	No other bias apparent.