• K K L Chan, B C P Chan, K F Lam, S Tam, and T T Lao.
• Department of Obstetrics and Gynaecology, University of Hong Kong, Hong Kong SAR, China. kklchan@hkucc.hku.hk
• BJOG. 2009 May 1;116(6):789-97; discussion 797-8.

ObjectiveTo test the hypothesis that iron supplement from early pregnancy would increase the risk of gestational diabetes mellitus (GDM).DesignRandomised placebo-controlled trial.SettingA university teaching hospital in Hong Kong.PopulationOne thousand one hundred sixty-four women with singleton pregnancy at less than 16 weeks of gestation with haemoglobin (Hb) level between 8 and 14 g/dl and no pre-existing diabetes or haemoglobinopathies.MethodsWomen were randomly allocated to receive 60 mg of iron supplement daily (n= 565) or placebo (n= 599). Oral glucose tolerance tests (OGTTs) were performed at 28 and 36 weeks. Women were followed up until delivery.Outcome MeasuresThe primary outcome was development of GDM at 28 weeks. The secondary outcomes were 2-hour post-OGTT glucose levels, development of GDM at 36 weeks and delivery and infant outcomes.ResultsThere was no significant difference in the incidence of GDM in the iron supplement and placebo groups at 28 weeks (OR: 1.04, 95% confidence interval [CI]: 0.7-1.53 at 90% power) or 36 weeks. Maternal Hb and ferritin levels were higher in the iron supplement group at delivery (P < 0.001 and P= 0.003, respectively). Elective caesarean section rate was lower in the iron supplement group (OR: 0.58, 95% CI: 0.37-0.89). Infant birthweight was heavier (P= 0.001), and there were fewer small-for-gestational-age babies in the iron supplement group (OR: 0.46, 95% CI: 0.24-0.85).ConclusionIron supplement from early pregnancy does not increase the risk of GDM. It may have benefits in terms of pregnancy outcomes.

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