The odds of moderate postpartum anemia (Hb < 90 g/L) with uncorrected iron deficiency in pregnancy (OR 7.7, 95% CI: 3.7–18.0), moderate anemia in pregnancy (OR 5.2, 95% CI: 1.1–49.9) and mild anemia in pregnancy (OR 3.2, 95% CI: 1.8–6.2) were significantly higher in transfused women relative to controls. This evidence concerns the gene GSTM1 and anemia.