Effect of iron supplementation on risk of maternal anaemia. Forest plot showing the RR of maternal anaemia between iron- and non-supplemented groups across 13 studies (n = 2315). The risk of anaemia was lower in the supplemented group (RR = 0.50, 95% CI = 0.34–0.74, P < .01). There was a moderate degree of heterogeneity (I² = 42%, tau² = 0.17).