Parenteral Iron Therapy in Pregnancy
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Direct answer
Parenteral iron therapy is intravenous iron given when oral iron fails, is not tolerated or cannot be absorbed, and it corrects anaemia faster in the second and third trimesters. Common agents are iron sucrose, ferric carboxymaltose and iron dextran, with ferric carboxymaltose needing fewer infusions. The dose is calculated from weight, haemoglobin and iron stores, and hypersensitivity and hypophosphataemia must be watched for.
What you must remember
- Indications: oral intolerance, malabsorption, failure to respond, or severe anaemia close to term, following current national guidance.
- Iron sucrose: given as several infusions in many regimens, with a long record of use in pregnancy.
- Ferric carboxymaltose: given as one or two infusions, with hypophosphataemia as a recognised effect.
- Iron dextran: higher anaphylaxis risk, so it is generally avoided.
- Ganzoni formula: total iron deficit in mg equals weight in kg multiplied by target minus actual haemoglobin in g/dL, multiplied by 2.4, plus iron stores of 500 mg for weight above 35 kg, often adjusted in pregnancy.
- Adverse reactions: hypersensitivity, hypotension, nausea, flushing and metallic taste, with observation for about 30 minutes after infusion.
- Diagnostic marker: ferritin below 30 μg/L indicates depleted stores, though inflammation can raise it.
Choosing an agent by its dosing pattern
A 28-year-old at 26 weeks has haemoglobin of 7.8 g/dL despite three months of oral iron. The choice of agent depends on how many visits and infusions a woman can manage, and on the safety profile of each preparation.
| Agent | Dosing pattern | Main concern |
|---|---|---|
| Iron sucrose | Several infusions per course | Hypotension and hypersensitivity |
| Ferric carboxymaltose | One or two infusions | Hypophosphataemia |
| Iron dextran | Single or split dose | Serious anaphylaxis |
Fewer infusions suit women who live far from a clinic, but the phosphate level should be checked afterwards. Iron dextran is generally avoided, and test doses do not reliably predict anaphylaxis.
Dose calculation is always done before the first infusion, and the total is then divided into individual infusions within the product's labelled maximum for a single dose. Observation facilities and resuscitation equipment should be in place, and the woman should be asked about any previous reaction to intravenous iron before treatment starts.
Where the exam tries to catch you
Parenteral iron questions test calculation and the logic of choosing a safer agent, not only the names of the drugs.
- Trap: "Give iron dextran after a negative test dose." Correct: test doses do not reliably predict anaphylaxis, so dextran is generally avoided.
- Trap: "A normal ferritin excludes iron deficiency in pregnancy." Correct: inflammation raises ferritin, so a normal value can hide depleted stores, and transferrin saturation helps.
- Trap: "Calculate the dose from haemoglobin alone." Correct: weight, target haemoglobin and iron stores are all needed in the calculation.
Frequently asked questions
When is intravenous iron preferred over oral iron in pregnancy?
Intravenous iron is preferred in pregnancy when oral iron is not tolerated, is poorly absorbed, has failed to correct haemoglobin, or when anaemia is severe late in pregnancy. Parenteral iron therapy is generally given in the second and third trimesters.
How is the total iron deficit calculated for intravenous iron?
The Ganzoni formula calculates total iron deficit as weight in kilograms multiplied by target minus actual haemoglobin, multiplied by 2.4, plus iron stores of 500 mg for weight above 35 kg. Many centres adjust the target and stores for pregnancy, so the local protocol should be followed.
Which intravenous iron preparation carries the highest anaphylaxis risk?
Iron dextran carries the highest risk of serious anaphylaxis among the commonly used intravenous iron preparations, which is why it is generally avoided. Iron sucrose and ferric carboxymaltose carry a lower risk of severe reactions, though observation after infusion is still needed.
What adverse reactions should be monitored after intravenous iron infusion?
Adverse reactions after intravenous iron include hypersensitivity, hypotension, nausea, flushing and metallic taste, and the woman should be observed for around 30 minutes with resuscitation available. Ferric carboxymaltose also needs phosphate monitoring, because hypophosphataemia can occur.