Singleton pregnant participants with moderate iron deficiency anaemia who are randomly assigned to an IV iron arm and receive, early in the second trimester of pregnancy, a single dose of IV iron for treatment of anaemia and the currently recommended daily dose of folic acid will have a higher conversion rate to non-anaemic status (or Hb >11 g/dL) in the last trimester of pregnancy at either a 30–34 week antenatal visit or prior to delivery than pregnant women assigned to an oral iron arm and provided a standard dose of iron and folic acid tablets for anaemia treatment. The gene discussed is GSTM1; the disease is anemia (phenotype).