GSTM1 and anemia (phenotype): During the delivery of pregnant women with anemia, the uterus would be hypoxic, which would lead to the loss of uterine muscle tension and the failure to contract blood vessels, resulting in massive blood loss.[22] The ID pregnant women with SF < 30 μg/L as the standard of preventive iron supplementation have a higher Hb level before delivery, and also reduce the occurrence of IDA before delivery, thereby reducing the incidence of postpartum hemorrhage.