Simmons 1993.

Methods	RCT, 3 arms with individual randomisation
Participants	376 pregnant women with ages between 16‐35 years, with mild anaemia (Hb concentrations between 80‐110 g/L) attending 8 maternal and child health centres in Kingston, St. Andrews and Spanish Town, Jamaica, with gestational age between 14‐22 weeks.
Interventions	Participants were randomly assigned to 1 of 3 groups: group 1 received 1 placebo tablet daily; group 2 received 100 mg of elemental iron (as ferrous sulphate) daily; group 3 received 50 mg of elemental iron (in a gastric delivery system capsule) daily. All women received 400 μg (0.4 mg) of folic acid. Setting and health worker cadre: the intervention was performed by clinic nurses and field workers at maternal and child health centres in urban areas of Jamaica.
Outcomes	Hb, HCT, MCV, white cell count, serum iron, total iron binding capacity, serum ferritin, serum transferrin receptor, at baseline, at 6 weeks and at 12 weeks after start of supplementation as well as side effects.
Notes	Gestational ages differed in the participants and we have not included outcome data from this trial in the review. Gestational age at start of supplementation: mixed gestational age (up to 22 weeks' gestation at recruitment). Anaemic status at start of supplementation: anaemic at the start of supplementation (mild anaemia Hb 80‐110 g/L). Daily iron dose: mixed dose (medium dose group ‐ 50 mg elemental iron in gastric delivery system capsule; higher dose group 100 mg of elemental iron). Iron release formulation: gastric delivery system capsule (controlled release preparation). Iron compound: ferrous sulphate. Malaria setting: yes. As of 2011: very limited risk of P. falciparum malaria may occur in the Kingston St Andrew Parish.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	By random number table.
Allocation concealment (selection bias)	Low risk	Sealed envelopes distributed to clinics (not clear if envelopes were opaque).
Blinding of participants and personnel (performance bias) All outcomes	High risk	Partial blinding. A placebo was provided but this was a single table while women in treatment groups received either 2 tablets or a capsule. It was stated that women were not told which preparations contained iron but staff would be aware of treatment.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Low risk for laboratory outcomes.
Incomplete outcome data (attrition bias) All outcomes	High risk	376 women were recruited. 275 women were followed up (73.1%) but laboratory results were available for 66% of the original sample.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Low risk	The 3 groups were reported to have similar characteristics at baseline.