In the screening group, more women were diagnosed with postpartum anaemia (adjusted OR 2.2 95%CI [1.6–3.0]); moderate-severe anaemia (defined as Hb ≤ 9.5 g/dL) was diagnosed more in the screening group, including in women with baseline Hb > 9.5 g/dL, compared with the symptoms group (adjusted OR 1.8 95%CI [1.3–2.6]). The gene discussed is GSTM1; the disease is anemia (phenotype).