Tholin 1993.

Methods	RCT, 3‐arm trial with individual randomisation.
Participants	83 healthy nulliparous non‐vegetarian, non‐anaemic pregnant women with serum ferritin concentrations above 10 μg/L.
Interventions	Participants were randomly assigned to 1 of 3 groups: group 1 received 100 mg of elemental iron (as ferrous sulphate) daily; group 2 received placebo; group 3 received dietary advice only. Setting and health worker cadre: the intervention was performed by physicians at the Maternal Health Unit of Ostersund Hospital in Ostersund, Sweden.
Outcomes	Blood Hb, serum ferritin and blood manganese were determined at baseline before 15th week of gestation, between 25‐28 weeks, and between 35‐40 weeks of gestation. Median and ranges are presented.
Notes	The aim of this study was to examine the relationship between iron and zinc levels during pregnancy. No outcomes were extractable from this report for this review. Median serum zinc levels were reported by randomisation group "levels did not differ between groups". Median Hb levels were reported for women who had normal vs complicated deliveries (rather than by randomisation group. Results for mean Hb and serum ferritin levels were depicted in graphs. Gestational age at start of supplementation: early gestational age at the start of supplementation (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)	Unclear risk	Described as "randomly assigned".
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double blind for iron supplemented group. Placebo‐controlled trial with outcome assessment by an obstetrician blind to group assignment.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Low risk for laboratory outcomes.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	There were some discrepancies in the figures reported in 2 study publications. (We have not included data from this trial in the review.)
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	High risk	Results were not simple to interpret and some results were not reported according to randomisation group.