Is allergen immunotherapy (allergy shots) safe during pregnancy?

Allergen Immunotherapy Safety in Pregnancy

Allergen immunotherapy can be safely continued during pregnancy if already at maintenance dose, but should not be initiated during pregnancy except in life-threatening cases of Hymenoptera (bee/wasp sting) anaphylaxis. 1, 2

Continuation of Existing Immunotherapy

If you are already on maintenance immunotherapy when pregnancy occurs, continue at your current dose without any increases. 1, 2

• Both subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) can be safely continued throughout pregnancy 2, 3
• Retrospective studies of over 400 pregnancies show no increased risk of prematurity, congenital malformations, hypertension, perinatal deaths, or other adverse pregnancy outcomes in women continuing immunotherapy 1, 2, 3
• A large Swedish nationwide study of 743 pregnancies exposed to AIT found no association with congenital malformations (OR 0.90) or adverse pregnancy outcomes including preterm birth, stillbirth, or cesarean delivery 4
• The dose must remain frozen at the current maintenance level—do not escalate or increase doses during pregnancy 1, 2, 5

Build-Up Phase Considerations

If pregnancy occurs during the build-up phase when you are receiving sub-therapeutic doses, strongly consider discontinuing immunotherapy. 1

• The risk-benefit calculation shifts unfavorably when doses are not yet therapeutic, as the patient receives minimal benefit while still facing potential systemic reaction risks 1
• This recommendation reflects the principle that continuation is justified only when therapeutic benefit is already established 1

Initiation During Pregnancy

Do not start allergen immunotherapy for the first time during pregnancy. 1, 2, 5

• The sole exception is life-threatening Hymenoptera anaphylaxis, where the mortality risk from future stings outweighs immunotherapy risks 2, 6
• The concern is not that immunotherapy itself causes fetal harm, but rather that systemic allergic reactions and their treatment (particularly epinephrine for anaphylaxis) could theoretically cause spontaneous abortion, premature labor, or fetal hypoxia 1, 2
• No large prospective studies have evaluated safety of immunotherapy initiation during pregnancy 1

Safety Evidence and Mechanisms

The safety profile is reassuring based on multiple lines of evidence:

• One retrospective study of 109 pregnant patients receiving immunotherapy versus 60 who refused showed higher rates of abortion, prematurity, and toxemia in the group that did not receive immunotherapy 1
• Another study of 121 pregnancies found adverse event rates similar to the general population, with actually higher abortion rates in the untreated atopic group 1
• Among the few women (10 out of 453 pregnancies) who experienced generalized reactions while receiving AIT, none had fetal complications 3
• Venom immunotherapy during pregnancy has demonstrated similar safety 1

Critical Safety Protocols During Pregnancy

Strict adherence to safety measures is non-negotiable when continuing immunotherapy during pregnancy:

• Ensure full observation period (typically 30 minutes) after each injection 2
• Report any symptoms immediately to healthcare providers 2
• Have injectable epinephrine immediately available at all times 2
• Any systemic reaction requires aggressive management, as maternal hypotension or hypoxia directly threatens fetal well-being 1, 2

Potential Benefits Beyond Symptom Control

Emerging evidence suggests immunotherapy during pregnancy may prevent allergic sensitization in offspring:

• One study demonstrated absence of allergen-specific IgE in paired cord blood 1
• Another showed inhibitory effects on immediate skin reactivity to grass allergens in some offspring 1
• Both studies found similar levels of allergen-specific IgG in cord blood and maternal blood samples 1
• However, more research is needed to confirm these preventive effects 6

Common Pitfalls to Avoid

• Never increase immunotherapy doses during pregnancy, even if the patient seems to be tolerating current doses well—this introduces unnecessary risk 1, 2
• Do not discontinue effective maintenance immunotherapy out of excessive caution—the evidence supports continuation, and uncontrolled allergic disease (especially asthma) poses definite risks to mother and fetus 1, 7
• Do not delay epinephrine if anaphylaxis occurs—there is no contraindication to epinephrine use in pregnancy when treating anaphylaxis, and maternal stabilization is the priority 6