Forty-eight randomised trials (17,793 women) and 44 cohort studies (1,851,682 women) were included. Eighteen randomised trials were classed as high quality.
Compared with controls, iron use (with or without folic acid) increased maternal mean haemoglobin (WMD 4.59g/L, 95% CI 3.72 to 5.46; Ι²=0%; 36 trials) and significantly reduced the risk of anaemia in the third trimester or at delivery (RR 0.50, 95% CI 0.42 to 0.59; Ι²=83%; 19 trials; a funnel plot suggested the presence of publication bias), iron deficiency (RR 0.59, 95% CI 0.44 to 0.79; Ι²=79%; eight trials), iron deficiency anaemia (RR 0.40, 95% CI 0.26 to 0.60; Ι²=33%; six trials) and low birth weight (RR 0.81, 95% CI 0.71 to 0.93; Ι²=1%; 13 trials). The effect of iron on preterm birth was not significant.
Analysis of cohort studies showed a significantly higher risk of low birth weight (adjusted OR 1.29, 95% CI 1.09 to 1.53; Ι²=90%; six studies) and preterm birth (adjusted OR 1.21, 95% CI 1.13 to 1.30; Ι²=0%; seven studies) with anaemia in the first or second trimester. Exposure-response analysis indicated that for every 10mg increase in iron dose/day up to 66mg/day, the relative risk of maternal anaemia was 0.88 (95% CI 0.84 to 0.92). Birth weight increased (WMD 15.1g, 95% CI 6.0 to 24.2; 18 trials) and risk of low birth weight decreased by 3% (RR 0.97, 95% CI 0.95 to 0.98; 13 trials) for every 10mg increase in dose/day. The linear trend was considered to be statistically significant. For each 1g/L increase in mean haemoglobin, birth weight increased by 14.0g (95% CI 6.8 to 21.8; 16 trials). No evidence of a significant effect was noted for duration of gestation, small for gestational age births and birth length.
Further results were reported.