Comparison of Oral Ferrous Sulfate to Intravenous Ferumoxytol in Antepartum Iron Deficiency Anemia

Evaluate the extent to which treatment of iron deficiency anemia beyond 24-34 weeks' gestation of pregnancy with intravenous iron increases hemoglobin compared to oral iron. The investigators will test the hypothesis that pregnant women who are anemic in the second and third trimester are more likely to significantly increase their hemoglobin with intravenous iron as opposed to the usual standard of care, oral iron.

Inclusion Criteria: 1. Pregnant women 18 years old and above 2. Hemoglobin \< 11 g/dL, serum ferritin \< 30 ug/dL and or transferrin saturation (TSAT) \< 20% 3. Between 24-34 weeks' pregnancy 4. Singleton pregnancy 5. Receiving prenatal care at Stanford/LPCH OB clinic and planning to deliver at LPCH 6. Hemodynamically stable Exclusion Criteria: 1. Patients unable to give informed consent 2. Known allergy/hypersensitivity to IV iron 3. Inflammatory Bowel Disease or history of gastric bypass surgery 4. Dialysis-dependent Chronic Kidney Disease/ ESRD 5. Known Hemoglobinopathies such as sickle cell disease, beta-thalassemia, alpha thalassemia 6. Folate/Vitamin B12 deficiency 7. Known malignancy 8. Medication allergy to Tylenol (acetaminophen) 9. Hemoglobin above 12 or less than 7 g/dL 10. Patients with complex past medical histories which may include history of multiple medication allergies (greater than 2 allergies), connective tissue disorder, etc. 11. Diagnosis of placenta previa