In plateau area, pregnant women with iron deficiency who start preventive iron supplementation with SF < 30 μg/L can reduce the incidence of iron deficiency and anemia before delivery compared with those who start preventive iron supplementation with Hb < 120 g/L, improve the level of Hb before delivery and the recovery rate and recovery time of SF ≥ 30 μg/L, and reduce the incidence of postpartum hemorrhage. Here, GSTM1 is linked to anemia (phenotype).