Ferrous Sulfate Dosing for Pregnant Patients
For routine supplementation in all pregnant women, prescribe 30 mg of elemental iron daily starting at the first prenatal visit; for treatment of confirmed iron deficiency anemia, prescribe 60-120 mg of elemental iron daily. 1
Prophylactic Supplementation (All Pregnant Women)
- Start 30 mg elemental iron daily at the first prenatal visit and continue throughout pregnancy 1, 2
- Standard prenatal vitamins typically contain 30-48 mg of elemental iron, which meets this prophylactic requirement 1, 2
- The Institute of Medicine's Recommended Dietary Allowance for iron in pregnancy is 27 mg per day, which aligns with this supplementation strategy 1
Treatment Dosing for Iron Deficiency Anemia
When iron deficiency anemia is confirmed (hemoglobin <11 g/dL with low ferritin), immediately prescribe 60-120 mg of elemental iron daily 1, 2
Practical Ferrous Sulfate Prescribing:
- Ferrous sulfate 325 mg tablets contain 65 mg elemental iron 2
- For treatment of anemia: prescribe 1-2 tablets daily (65-130 mg elemental iron) 1, 2
- Alternative formulations: ferrous fumarate 210 mg or ferrous gluconate 300 mg provide similar elemental iron content 1
High-Risk Populations Requiring Higher Doses
Women at increased risk for iron deficiency should receive 60-100 mg elemental iron daily from early pregnancy 1
Risk factors include:
- Non-Hispanic Black or Mexican American ethnicity (higher prevalence of iron deficiency) 1, 2
- Vegetarian diet (may require almost twice as much iron due to poor absorption of non-heme iron) 1, 2
- Short interval between pregnancies 1, 2
- Gastrointestinal conditions or medications that decrease iron absorption (e.g., antacids) 1, 2
- Multiparity (≥2 previous pregnancies) 1
Optimizing Absorption and Minimizing Side Effects
- Take iron supplements at bedtime to reduce gastrointestinal side effects 2
- Separate calcium supplements and antacids from iron by 1-2 hours, as they significantly decrease iron absorption 1, 3, 2
- Encourage taking iron with vitamin C-containing foods or citrus drinks to enhance absorption 1, 2
- If gastrointestinal side effects occur (nausea, constipation), consider splitting the dose or switching formulations 3
Monitoring and Treatment Response
- Recheck hemoglobin or hematocrit after 4 weeks of treatment 1, 4, 2
- Expected response: hemoglobin should increase by ≥1 g/dL or hematocrit by ≥3% 4, 2
- Once hemoglobin normalizes for gestational age, decrease to prophylactic dose of 30 mg/day 2
- Continue treatment for 2-3 months after hemoglobin normalizes to replenish iron stores 4, 2
When Oral Iron Fails:
- If hemoglobin fails to increase by ≥1 g/dL after 4 weeks despite compliance, obtain MCV, RDW, and serum ferritin 4, 2
- Consider alternative diagnoses such as thalassemia minor or sickle cell trait, particularly in women of African, Mediterranean, or Southeast Asian ancestry 2
- Refer to a physician if hemoglobin <9.0 g/dL or hematocrit <27.0% 2
- Intravenous iron may be considered as second-line therapy for non-responders 1
Postpartum Management
- Discontinue routine iron supplementation at delivery if no anemia or risk factors are present 4, 2
- Screen for anemia at 4-6 weeks postpartum only if risk factors exist: anemia continued through third trimester, excessive blood loss at delivery, or multiple birth 4, 2
- If postpartum iron deficiency anemia is diagnosed, treat with 60-120 mg elemental iron daily for 2-3 months after hemoglobin normalizes 4, 2
Common Pitfalls to Avoid
- Failing to separate calcium supplements and antacids from iron doses (this is the most common reason for treatment failure) 1, 3, 2
- Not identifying high-risk women who need increased supplementation (60-100 mg daily) from early pregnancy rather than standard 30 mg 1, 2
- Discontinuing treatment too early before iron stores are replenished 4, 2
- Relying solely on hemoglobin levels, as hemoglobin can be normal despite depleted iron stores 3