Chan 2009.

Methods	RCT (placebo controlled) 2‐arm trial, individual randomisation.
Participants	1164 pregnant women with singleton pregnancies with a gestational age of 16 weeks or less able to understand English or Chinese attending their first antenatal care visit at Queen Mary Hospital, Hong Kong between April 2005 and March 2007. Exclusion criteria: women with existing diabetes, haemoglobinopathies, Hb levels  < 80 g/L or > 140 g/L, women with possible thalassaemia (MCV < 80), women diagnosed with gestational diabetes at booking.
Interventions	Participants were randomly assigned to 1 of 2 groups: group 1: (n = 565 women) received 60 mg of elemental iron orally (as 300 mg ferrous sulphate) daily; group 2: (n = 599 women) received daily placebo indistinguishable in appearance from the active supplements. Women in both groups were provided with a supply for 16 weeks. At 28‐30 weeks further supplements were provided (up to 36 weeks) as long as women had not developed gestational diabetes mellitus or Hb level was > 140 g/L. If women in the placebo group developed anaemia (Hb < 80 g/L), they were given iron supplements as clinically indicated. Baseline investigations included a full blood count including Hb and HCT, MCV, white cells and platelets along with serum ferritin concentration. A OGIT was carried out at baseline for women with risk factors for gestational diabetes (e.g. advanced maternal age, family history of diabetes).  Otherwise women in both groups received standard antenatal care. Setting and health worker cadre: the intervention was performed by physicians at a regional university teaching hospital in Hong Kong.
Outcomes	Follow‐up at 28 weeks and 36 weeks' gestation and delivery and 3 days postpartum. Main outcome: development of gestational diabetes at 28 or 36 weeks.  (According to WHO criteria for impaired glucose tolerance test (OGTT 2‐hour value > or = 7.8 < 11.1 mmol/L) or diabetes (OGTT 2‐hour value > or = 11.1 mmol) both were considered as gestational diabetes mellitus). Other maternal outcomes: Hb (g/L), serum transferrin (g/L), serum ferritin (pmol/L), compliance, glucose level, mode of delivery. Neonatal outcomes: gestational age at delivery, preterm delivery, birthweight, Apgar score at 1 and 5 minutes, arterial blood pH, Hb of cord blood (g/L), ferritin of cord blood (pmol/L), jaundice, birth trauma, infection, congenital abnormality or metabolic disorder.
Notes	Very high attrition (> 50% for outcomes at 36 weeks).  45.6% of controls and 43.1% of women in the study group were taking additional vitamin supplements. As the results reported in the paper were not completely clear to us we preferred not to use the reported SDs and removed the information from this trial for continuous variables, while awaiting clarification from the authors. Gestational age at start of supplementation: early gestational age (supplementation started before 20 weeks) (16 weeks or less). Anaemic status at start of supplementation: mixed anaemia status (Hb levels > 80 and < 140 g/L). Daily iron dose: higher dose (60 mg elemental iron). Iron release formulation:normal release iron supplement/not specified. Iron compound: ferrous sulphate. Malaria setting: yes. As of 2011: Malaria risk, including P. falciparum malaria, exists in Yunnan and to a lesser extent in Hainan. P. falciparum resistance to chloroquine and sulphadoxine–pyrimethamine reported. Limited risk of P. vivax malaria exists in southern and some central provinces, including Anhui, Ghuizhou, Henan, Hubei, Jiangsu. There is no malaria risk in urban areas.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was carried out by a research nurse who was not involved in patient recruitment. Block randomisation with computer generation of sequence.  The block size was 100.
Allocation concealment (selection bias)	Low risk	Sealed opaque envelopes. The envelopes were sequentially numbered and sealed (by nurse A who did the block randomisation) and all the envelopes were accounted for.  The research assistant who recruited the patients (nurse B) would sequentially open the numbered envelopes after the patient had consented to participate in the study.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Participants blinded; placebo‐controlled. After randomisation “The participants but not the research assistants were blinded to group assignment”. Staff and research nurses were aware of the group allocation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcomes were assessed by the principle investigator (the outcomes are mainly objective outcomes such as OGTT results, blood counts, birthweight, etc).Women who developed anaemia were treated and those developing gestational diabetes withdrawn. Compliance, side effect and other outcomes reported as well as laboratory outcomes.
Incomplete outcome data (attrition bias) All outcomes	High risk	1164 women were randomised. It was stated that an ITT analysis was performed but data tables suggest there were missing data for most outcomes at 28 and 36 weeks and at delivery; e.g. at 28 weeks 90.3% attended for follow‐up. Neonatal outcome data were available for 74% of those randomised. There were very high levels (> 50%) of missing data for lab values at 36 weeks.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information to permit judgement.
Other bias	Low risk	No baseline imbalance between groups apparent.