In this study conducted in a large maternity unit in Singapore between 2021 to 2023, we compared the changes in maternal hematological parameters among obstetric patients with iron deficiency anemia presenting to the day care unit in the second or third trimester with a Hb level of <8 g/dl treated with a single dose of ferric carboxymaltose injection (Ferinject) against a control group who were referred for treatment but defaulted on and declined treatment. Here, GSTM1 is linked to Iron deficiency anemia.