Iron Infusion Thresholds in Pregnancy
Iron infusion in pregnancy should be reserved for severe iron deficiency anemia (ferritin ≤15 ng/mL with confirmed anemia) when oral iron is not tolerated, ineffective, or contraindicated—not based on ferritin levels alone. 1
Diagnostic Criteria for Iron Deficiency in Pregnancy
The decision to use intravenous iron requires both anemia and confirmed iron deficiency:
- Ferritin ≤15 μg/L (ng/mL) confirms iron deficiency in pregnant women with anemia 1
- Hemoglobin thresholds for anemia vary by trimester due to physiologic hemodilution 1
- Ferritin alone should not trigger IV iron therapy without documented anemia 1
When IV Iron Is Indicated
Intravenous iron administration is appropriate when:
- Severe iron deficiency anemia is confirmed (ferritin ≤15 ng/mL with anemia) AND one of the following conditions exists 2:
- Severe side effects from oral iron preparations preventing compliance
- Lack of improvement despite adequate oral iron intake
- History of gastrointestinal surgery affecting iron absorption
- Clinical urgency requiring rapid hemoglobin restoration
Important Clinical Context
Ferritin levels naturally decline during pregnancy even with adequate iron stores, reaching mean values of 11.8 ng/mL by the third trimester in physiologic pregnancy 3. This physiologic decline does not automatically warrant IV iron.
Standard oral supplementation (27 mg elemental iron in prenatal vitamins) is sufficient for most pregnant women with adequate baseline iron stores 1. Additional supplementation beyond standard prenatal vitamins provides no demonstrated benefit when iron stores are already adequate 1.
Safety and Efficacy Data
When IV iron is appropriately indicated, it effectively regenerates hemoglobin and iron stores 2:
- Mean hemoglobin increased from 8.4 g/dL to 10.1 g/dL at therapy completion, continuing to rise to 10.9 g/dL two weeks later 2
- Ferritin levels increased from 2.9 ng/mL to 122.8 ng/mL at therapy completion 2
- Only mild and transient side effects were reported, with one patient (4%) developing urticaria after test dose 2
Critical Pitfalls to Avoid
Do not use ferritin levels in isolation to determine need for IV iron 1. Ferritin is an acute phase reactant and may be falsely elevated during inflammation or infection, potentially masking true iron deficiency 1.
Do not assume low ferritin alone requires IV iron. The threshold of ≤15 μg/L must be accompanied by documented anemia to justify IV iron therapy 1.
Recognize that hemoglobin naturally decreases during pregnancy due to physiologic hemodilution—a hemoglobin of 11.8 g/dL is considered normal and does not indicate anemia 1.
Monitoring Approach
For pregnant women receiving IV iron 4:
- Evaluate complete blood count and iron parameters (ferritin, transferrin saturation) 4-8 weeks after the last infusion
- Do not check iron parameters within 4 weeks of total dose infusion, as circulating iron interferes with assays
- Hemoglobin should increase by 1-2 g/dL within 4-8 weeks of therapy
- Target ferritin is 50 ng/mL in the absence of inflammation 4