Can iron injections cause mild pains in pregnancy?

Can Intravenous Iron Cause Mild Pains in Pregnancy?

Yes, intravenous iron can cause mild pains during pregnancy, most commonly presenting as myalgias, arthralgias, back pain, or chest pressure as part of a non-allergic infusion reaction that typically resolves without treatment. 1

Understanding the Mechanism of Pain

The mild pains experienced with IV iron are most likely due to complement activation-related pseudo-allergy (CARPA), not a true allergic reaction. 1 This reaction occurs when:

• Labile free iron (weakly bound iron released from the iron carbohydrate nanoparticle) triggers a complement-mediated response 1
• The reaction is non-life threatening and can occur without prior sensitization 1
• Symptoms most frequently appear at the beginning of the infusion 1

Specific Pain Presentations

Common pain-related symptoms include:

• Myalgias and/or arthralgias (muscle and joint pains) 1
• Back pain 1, 2
• Chest pressure (not chest pain with cardiac features) 1
• Injection site pain 2, 3
• Abdominal pain (though this warrants closer monitoring as it can indicate anaphylaxis) 3

Distinguishing Safe Reactions from Dangerous Ones

Critical distinction: These mild pains are NOT accompanied by signs of true anaphylaxis. 1 You must immediately intervene if the patient develops:

• Systemic hypotension 1, 4
• Wheezing 1, 4
• Peri-orbital edema 1, 4
• Respiratory stridor or airway compromise 1, 4
• Gastrointestinal pain (as opposed to mild discomfort) 1, 4

Management of Mild Pain Reactions

When mild pains occur during infusion:

• Slow or temporarily stop the infusion 4
• Most reactions resolve without treatment 1, 4
• Continue observation for at least 30 minutes post-infusion 5, 4
• Resuscitation facilities must be immediately available 5, 4

Important: Premedication is NOT routinely recommended and should be reserved only for patients at high risk of hypersensitivity reactions. 4

Pregnancy-Specific Considerations

IV iron administration in pregnancy has specific safety parameters:

• Avoid IV iron before 13 weeks gestation due to lack of safety data 1, 4
• After 13 weeks, administration is the same as in non-pregnant patients 1
• Fetal monitoring during or after IV iron is NOT required and NOT recommended 1, 4
• Severe hypersensitivity reactions (though extremely rare at <1 in 200,000) can cause fetal bradycardia 4, 2

Formulation Differences

The type of IV iron affects the likelihood of reactions:

• Ferric gluconate and iron sucrose release larger amounts of labile free iron, requiring lower doses and more frequent visits 1
• Ferric derisomaltose (Monoferric) has significantly lower rates of serious reactions (0.14%) compared to ferric carboxymaltose (1.08%) 4
• True IgE-mediated anaphylaxis is exceedingly rare, occurring in less than 1 in 200,000 administrations 4

Common Pitfalls to Avoid

• Do not confuse CARPA with true anaphylaxis - the former is self-limited and benign, while the latter requires emergency intervention 1
• Do not routinely premedicate - this is not evidence-based and should only be used in high-risk patients 4
• Do not order fetal monitoring for routine IV iron administration in pregnancy 1, 4
• Do not avoid IV iron in pregnancy after 13 weeks - it is safe and effective when oral iron fails 1, 6